lecture 13
DESCRIPTION
Lecture 13. Computer Networking: A Top Down Approach 6 th edition Jim Kurose, Keith Ross Addison-Wesley March 2012. CS3516: These slides are generated from those made available by the authors of our text. - PowerPoint PPT PresentationTRANSCRIPT
Introduction 1-1
Lecture 13
Computer Networking A Top Down Approach 6th edition Jim Kurose Keith RossAddison-WesleyMarch 2012
CS3516
These slides are generated from those made available by the authors of our text
Network Layer 4-2
Get MAC Address (Getmacexe) Discovers the Media Access Control (MAC) address and lists associated network protocols for all network cards in a computer either locally or across a network
CUsersjbgtgetmacPhysical Address Transport Name============ =============================60-36-DD-AA-13-69 Media disconnected60-36-DD-AA-13-65 DeviceTcpip_437F350E-DFD7-4A86-B063-0B9650BD440460-36-DD-AA-13-66 Media disconnected60-36-DD-AA-13-66 Media disconnectedB8-CA-3A-DC-C6-2B Media disconnected08-00-27-00-E4-38 DeviceTcpip_F551D578-DC71-4760-B91C-B349EAE4238F
Useful Commands
Network Layer 4-3
IP Configuration Utility (Ipconfigexe) Displays all current (TCPIP) network configurations
CUsersjbgtipconfig
Windows IP ConfigurationEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Link-local IPv6 Address fe80e59174d4a495799816 IPv4 Address 1302152836 Subnet Mask 2552552480 Default Gateway 130215241
CUsersjbgtipconfig Prints command line options
CUsersjbgtipconfig displaydns gives dns info cached on nodecswpiedu ---------------------------------------- Record Name cswpiedu Record Type 1 Time To Live 73497 Data Length 4 Section Answer A (Host) Record 13021528181
Useful Commands
Network Layer 4-4
Name Server Lookup (Nslookupexe) Displays information about Domain Name System records for specific IP addresses andor host names so that you can troubleshoot DNS problems
CUsersjbgtnslookup wwwgooglecomServer aresolverslevel3net this is the name of the default serverAddress 4221
Non-authoritative answerName wwwgooglecomAddresses 2607f8b040008041011 74125227179 74125227180 74125227176 74125227177 74125227178
Useful Commands
Network Layer 4-5
Net services commands (Netexe) Performs a broad range of network tasks Type net with no parameters to see a full list of available command-line options
CUsersjbgtnet helpThe syntax of this command is
Commands available are
NET ACCOUNTS NET HELPMSG NET STATISTICS NET COMPUTER NET LOCALGROUP NET STOP NET CONFIG NET PAUSE NET TIME NET CONTINUE NET SESSION NET USE NET FILE NET SHARE NET USER NET GROUP NET START NET VIEW NET HELP
NET HELP NAMES explains different types of names in NET HELP syntax lines
NET HELP SERVICES lists some of the services you can start NET HELP SYNTAX explains how to read NET HELP syntax lines NET HELP command | MORE displays Help one screen at a time
Useful Commands
Network Layer 4-6
Netstat (Netstatexe) Displays active TCP connections ports on which the computer is listening Ethernet statistics the IP routing table and IPv4IPv6 statistics
CUsersjbgtnetstat
Proto Local Address Foreign Address State TCP 1270011029 jb-laptop5354 ESTABLISHED TCP 1270011036 jb-laptop27015 ESTABLISHED TCP 1270011047 jb-laptop19872 ESTABLISHED TCP 12700139055 jb-laptop39054 ESTABLISHED TCP 172171681382492 blugro5relay2492 ESTABLISHED
CUsersjbgtnetstat -sIPv4 Statistics Packets Received = 10158258 Received Header Errors = 2848 Received Address Errors = 2192434 Datagrams Forwarded = 0 Unknown Protocols Received = 170614 Received Packets Discarded = 4173788 Received Packets Delivered = 6692404
Useful Commands
Network Layer 4-7
Network Command Shell (Netshexe) Displays or modifies the network configuration of a local or remote computer that is currently running This command-line scripting utility has a huge number of options which are fully detailed in Help
TCPIP Route (Routeexe) Displays and modifies entries in the local IP routing table
CUsersjbgtroute printInterface List1360 36 dd aa 13 65 Intel(R) Centrino(R) Wireless-N 22301260 36 dd aa 13 69 Bluetooth Device (Personal Area Network)3108 00 27 00 e4 38 VirtualBox Host-Only Ethernet Adapter
IPv4 Route TableNetwork Destination Netmask Gateway Interface Metric 0000 0000 1721711 17217168138 25 127000 255000 On-link 127001 306 127001 255255255255 On-link 127001 306 127255255255 255255255255 On-link 127001 306 16925400 25525500 On-link 16925440182 276 16925440182 255255255255 On-link 16925440182 276 169254255255 255255255255 On-link 16925440182 276 1721700 25525500 On-link 17217168138 281 17217168138 255255255255 On-link 17217168138 281 17217255255 255255255255 On-link 17217168138 281 224000 240000 On-link 16925440182 276
Useful Commands
Network Layer 4-8
(Arpexe) Displays current ARP entries by interrogating the current protocol data If inet_addr is specified the IP and Physical addresses for only the specified computer are displayed If more than one network interface uses ARP entries for each ARP table are displayed
CUsersjbgtarp -a
Interface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527252 f0-1f-af-2f-e1-27 dynamic 1302152863 00-16-3e-c5-01-25 dynamic 13021529165 00-24-e8-32-32-1d dynamic 13021531255 ff-ff-ff-ff-ff-ff static
Useful Commands
Link Layer 5-9
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Network Layer 4-2
Get MAC Address (Getmacexe) Discovers the Media Access Control (MAC) address and lists associated network protocols for all network cards in a computer either locally or across a network
CUsersjbgtgetmacPhysical Address Transport Name============ =============================60-36-DD-AA-13-69 Media disconnected60-36-DD-AA-13-65 DeviceTcpip_437F350E-DFD7-4A86-B063-0B9650BD440460-36-DD-AA-13-66 Media disconnected60-36-DD-AA-13-66 Media disconnectedB8-CA-3A-DC-C6-2B Media disconnected08-00-27-00-E4-38 DeviceTcpip_F551D578-DC71-4760-B91C-B349EAE4238F
Useful Commands
Network Layer 4-3
IP Configuration Utility (Ipconfigexe) Displays all current (TCPIP) network configurations
CUsersjbgtipconfig
Windows IP ConfigurationEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Link-local IPv6 Address fe80e59174d4a495799816 IPv4 Address 1302152836 Subnet Mask 2552552480 Default Gateway 130215241
CUsersjbgtipconfig Prints command line options
CUsersjbgtipconfig displaydns gives dns info cached on nodecswpiedu ---------------------------------------- Record Name cswpiedu Record Type 1 Time To Live 73497 Data Length 4 Section Answer A (Host) Record 13021528181
Useful Commands
Network Layer 4-4
Name Server Lookup (Nslookupexe) Displays information about Domain Name System records for specific IP addresses andor host names so that you can troubleshoot DNS problems
CUsersjbgtnslookup wwwgooglecomServer aresolverslevel3net this is the name of the default serverAddress 4221
Non-authoritative answerName wwwgooglecomAddresses 2607f8b040008041011 74125227179 74125227180 74125227176 74125227177 74125227178
Useful Commands
Network Layer 4-5
Net services commands (Netexe) Performs a broad range of network tasks Type net with no parameters to see a full list of available command-line options
CUsersjbgtnet helpThe syntax of this command is
Commands available are
NET ACCOUNTS NET HELPMSG NET STATISTICS NET COMPUTER NET LOCALGROUP NET STOP NET CONFIG NET PAUSE NET TIME NET CONTINUE NET SESSION NET USE NET FILE NET SHARE NET USER NET GROUP NET START NET VIEW NET HELP
NET HELP NAMES explains different types of names in NET HELP syntax lines
NET HELP SERVICES lists some of the services you can start NET HELP SYNTAX explains how to read NET HELP syntax lines NET HELP command | MORE displays Help one screen at a time
Useful Commands
Network Layer 4-6
Netstat (Netstatexe) Displays active TCP connections ports on which the computer is listening Ethernet statistics the IP routing table and IPv4IPv6 statistics
CUsersjbgtnetstat
Proto Local Address Foreign Address State TCP 1270011029 jb-laptop5354 ESTABLISHED TCP 1270011036 jb-laptop27015 ESTABLISHED TCP 1270011047 jb-laptop19872 ESTABLISHED TCP 12700139055 jb-laptop39054 ESTABLISHED TCP 172171681382492 blugro5relay2492 ESTABLISHED
CUsersjbgtnetstat -sIPv4 Statistics Packets Received = 10158258 Received Header Errors = 2848 Received Address Errors = 2192434 Datagrams Forwarded = 0 Unknown Protocols Received = 170614 Received Packets Discarded = 4173788 Received Packets Delivered = 6692404
Useful Commands
Network Layer 4-7
Network Command Shell (Netshexe) Displays or modifies the network configuration of a local or remote computer that is currently running This command-line scripting utility has a huge number of options which are fully detailed in Help
TCPIP Route (Routeexe) Displays and modifies entries in the local IP routing table
CUsersjbgtroute printInterface List1360 36 dd aa 13 65 Intel(R) Centrino(R) Wireless-N 22301260 36 dd aa 13 69 Bluetooth Device (Personal Area Network)3108 00 27 00 e4 38 VirtualBox Host-Only Ethernet Adapter
IPv4 Route TableNetwork Destination Netmask Gateway Interface Metric 0000 0000 1721711 17217168138 25 127000 255000 On-link 127001 306 127001 255255255255 On-link 127001 306 127255255255 255255255255 On-link 127001 306 16925400 25525500 On-link 16925440182 276 16925440182 255255255255 On-link 16925440182 276 169254255255 255255255255 On-link 16925440182 276 1721700 25525500 On-link 17217168138 281 17217168138 255255255255 On-link 17217168138 281 17217255255 255255255255 On-link 17217168138 281 224000 240000 On-link 16925440182 276
Useful Commands
Network Layer 4-8
(Arpexe) Displays current ARP entries by interrogating the current protocol data If inet_addr is specified the IP and Physical addresses for only the specified computer are displayed If more than one network interface uses ARP entries for each ARP table are displayed
CUsersjbgtarp -a
Interface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527252 f0-1f-af-2f-e1-27 dynamic 1302152863 00-16-3e-c5-01-25 dynamic 13021529165 00-24-e8-32-32-1d dynamic 13021531255 ff-ff-ff-ff-ff-ff static
Useful Commands
Link Layer 5-9
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Network Layer 4-3
IP Configuration Utility (Ipconfigexe) Displays all current (TCPIP) network configurations
CUsersjbgtipconfig
Windows IP ConfigurationEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Link-local IPv6 Address fe80e59174d4a495799816 IPv4 Address 1302152836 Subnet Mask 2552552480 Default Gateway 130215241
CUsersjbgtipconfig Prints command line options
CUsersjbgtipconfig displaydns gives dns info cached on nodecswpiedu ---------------------------------------- Record Name cswpiedu Record Type 1 Time To Live 73497 Data Length 4 Section Answer A (Host) Record 13021528181
Useful Commands
Network Layer 4-4
Name Server Lookup (Nslookupexe) Displays information about Domain Name System records for specific IP addresses andor host names so that you can troubleshoot DNS problems
CUsersjbgtnslookup wwwgooglecomServer aresolverslevel3net this is the name of the default serverAddress 4221
Non-authoritative answerName wwwgooglecomAddresses 2607f8b040008041011 74125227179 74125227180 74125227176 74125227177 74125227178
Useful Commands
Network Layer 4-5
Net services commands (Netexe) Performs a broad range of network tasks Type net with no parameters to see a full list of available command-line options
CUsersjbgtnet helpThe syntax of this command is
Commands available are
NET ACCOUNTS NET HELPMSG NET STATISTICS NET COMPUTER NET LOCALGROUP NET STOP NET CONFIG NET PAUSE NET TIME NET CONTINUE NET SESSION NET USE NET FILE NET SHARE NET USER NET GROUP NET START NET VIEW NET HELP
NET HELP NAMES explains different types of names in NET HELP syntax lines
NET HELP SERVICES lists some of the services you can start NET HELP SYNTAX explains how to read NET HELP syntax lines NET HELP command | MORE displays Help one screen at a time
Useful Commands
Network Layer 4-6
Netstat (Netstatexe) Displays active TCP connections ports on which the computer is listening Ethernet statistics the IP routing table and IPv4IPv6 statistics
CUsersjbgtnetstat
Proto Local Address Foreign Address State TCP 1270011029 jb-laptop5354 ESTABLISHED TCP 1270011036 jb-laptop27015 ESTABLISHED TCP 1270011047 jb-laptop19872 ESTABLISHED TCP 12700139055 jb-laptop39054 ESTABLISHED TCP 172171681382492 blugro5relay2492 ESTABLISHED
CUsersjbgtnetstat -sIPv4 Statistics Packets Received = 10158258 Received Header Errors = 2848 Received Address Errors = 2192434 Datagrams Forwarded = 0 Unknown Protocols Received = 170614 Received Packets Discarded = 4173788 Received Packets Delivered = 6692404
Useful Commands
Network Layer 4-7
Network Command Shell (Netshexe) Displays or modifies the network configuration of a local or remote computer that is currently running This command-line scripting utility has a huge number of options which are fully detailed in Help
TCPIP Route (Routeexe) Displays and modifies entries in the local IP routing table
CUsersjbgtroute printInterface List1360 36 dd aa 13 65 Intel(R) Centrino(R) Wireless-N 22301260 36 dd aa 13 69 Bluetooth Device (Personal Area Network)3108 00 27 00 e4 38 VirtualBox Host-Only Ethernet Adapter
IPv4 Route TableNetwork Destination Netmask Gateway Interface Metric 0000 0000 1721711 17217168138 25 127000 255000 On-link 127001 306 127001 255255255255 On-link 127001 306 127255255255 255255255255 On-link 127001 306 16925400 25525500 On-link 16925440182 276 16925440182 255255255255 On-link 16925440182 276 169254255255 255255255255 On-link 16925440182 276 1721700 25525500 On-link 17217168138 281 17217168138 255255255255 On-link 17217168138 281 17217255255 255255255255 On-link 17217168138 281 224000 240000 On-link 16925440182 276
Useful Commands
Network Layer 4-8
(Arpexe) Displays current ARP entries by interrogating the current protocol data If inet_addr is specified the IP and Physical addresses for only the specified computer are displayed If more than one network interface uses ARP entries for each ARP table are displayed
CUsersjbgtarp -a
Interface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527252 f0-1f-af-2f-e1-27 dynamic 1302152863 00-16-3e-c5-01-25 dynamic 13021529165 00-24-e8-32-32-1d dynamic 13021531255 ff-ff-ff-ff-ff-ff static
Useful Commands
Link Layer 5-9
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Network Layer 4-4
Name Server Lookup (Nslookupexe) Displays information about Domain Name System records for specific IP addresses andor host names so that you can troubleshoot DNS problems
CUsersjbgtnslookup wwwgooglecomServer aresolverslevel3net this is the name of the default serverAddress 4221
Non-authoritative answerName wwwgooglecomAddresses 2607f8b040008041011 74125227179 74125227180 74125227176 74125227177 74125227178
Useful Commands
Network Layer 4-5
Net services commands (Netexe) Performs a broad range of network tasks Type net with no parameters to see a full list of available command-line options
CUsersjbgtnet helpThe syntax of this command is
Commands available are
NET ACCOUNTS NET HELPMSG NET STATISTICS NET COMPUTER NET LOCALGROUP NET STOP NET CONFIG NET PAUSE NET TIME NET CONTINUE NET SESSION NET USE NET FILE NET SHARE NET USER NET GROUP NET START NET VIEW NET HELP
NET HELP NAMES explains different types of names in NET HELP syntax lines
NET HELP SERVICES lists some of the services you can start NET HELP SYNTAX explains how to read NET HELP syntax lines NET HELP command | MORE displays Help one screen at a time
Useful Commands
Network Layer 4-6
Netstat (Netstatexe) Displays active TCP connections ports on which the computer is listening Ethernet statistics the IP routing table and IPv4IPv6 statistics
CUsersjbgtnetstat
Proto Local Address Foreign Address State TCP 1270011029 jb-laptop5354 ESTABLISHED TCP 1270011036 jb-laptop27015 ESTABLISHED TCP 1270011047 jb-laptop19872 ESTABLISHED TCP 12700139055 jb-laptop39054 ESTABLISHED TCP 172171681382492 blugro5relay2492 ESTABLISHED
CUsersjbgtnetstat -sIPv4 Statistics Packets Received = 10158258 Received Header Errors = 2848 Received Address Errors = 2192434 Datagrams Forwarded = 0 Unknown Protocols Received = 170614 Received Packets Discarded = 4173788 Received Packets Delivered = 6692404
Useful Commands
Network Layer 4-7
Network Command Shell (Netshexe) Displays or modifies the network configuration of a local or remote computer that is currently running This command-line scripting utility has a huge number of options which are fully detailed in Help
TCPIP Route (Routeexe) Displays and modifies entries in the local IP routing table
CUsersjbgtroute printInterface List1360 36 dd aa 13 65 Intel(R) Centrino(R) Wireless-N 22301260 36 dd aa 13 69 Bluetooth Device (Personal Area Network)3108 00 27 00 e4 38 VirtualBox Host-Only Ethernet Adapter
IPv4 Route TableNetwork Destination Netmask Gateway Interface Metric 0000 0000 1721711 17217168138 25 127000 255000 On-link 127001 306 127001 255255255255 On-link 127001 306 127255255255 255255255255 On-link 127001 306 16925400 25525500 On-link 16925440182 276 16925440182 255255255255 On-link 16925440182 276 169254255255 255255255255 On-link 16925440182 276 1721700 25525500 On-link 17217168138 281 17217168138 255255255255 On-link 17217168138 281 17217255255 255255255255 On-link 17217168138 281 224000 240000 On-link 16925440182 276
Useful Commands
Network Layer 4-8
(Arpexe) Displays current ARP entries by interrogating the current protocol data If inet_addr is specified the IP and Physical addresses for only the specified computer are displayed If more than one network interface uses ARP entries for each ARP table are displayed
CUsersjbgtarp -a
Interface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527252 f0-1f-af-2f-e1-27 dynamic 1302152863 00-16-3e-c5-01-25 dynamic 13021529165 00-24-e8-32-32-1d dynamic 13021531255 ff-ff-ff-ff-ff-ff static
Useful Commands
Link Layer 5-9
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Network Layer 4-5
Net services commands (Netexe) Performs a broad range of network tasks Type net with no parameters to see a full list of available command-line options
CUsersjbgtnet helpThe syntax of this command is
Commands available are
NET ACCOUNTS NET HELPMSG NET STATISTICS NET COMPUTER NET LOCALGROUP NET STOP NET CONFIG NET PAUSE NET TIME NET CONTINUE NET SESSION NET USE NET FILE NET SHARE NET USER NET GROUP NET START NET VIEW NET HELP
NET HELP NAMES explains different types of names in NET HELP syntax lines
NET HELP SERVICES lists some of the services you can start NET HELP SYNTAX explains how to read NET HELP syntax lines NET HELP command | MORE displays Help one screen at a time
Useful Commands
Network Layer 4-6
Netstat (Netstatexe) Displays active TCP connections ports on which the computer is listening Ethernet statistics the IP routing table and IPv4IPv6 statistics
CUsersjbgtnetstat
Proto Local Address Foreign Address State TCP 1270011029 jb-laptop5354 ESTABLISHED TCP 1270011036 jb-laptop27015 ESTABLISHED TCP 1270011047 jb-laptop19872 ESTABLISHED TCP 12700139055 jb-laptop39054 ESTABLISHED TCP 172171681382492 blugro5relay2492 ESTABLISHED
CUsersjbgtnetstat -sIPv4 Statistics Packets Received = 10158258 Received Header Errors = 2848 Received Address Errors = 2192434 Datagrams Forwarded = 0 Unknown Protocols Received = 170614 Received Packets Discarded = 4173788 Received Packets Delivered = 6692404
Useful Commands
Network Layer 4-7
Network Command Shell (Netshexe) Displays or modifies the network configuration of a local or remote computer that is currently running This command-line scripting utility has a huge number of options which are fully detailed in Help
TCPIP Route (Routeexe) Displays and modifies entries in the local IP routing table
CUsersjbgtroute printInterface List1360 36 dd aa 13 65 Intel(R) Centrino(R) Wireless-N 22301260 36 dd aa 13 69 Bluetooth Device (Personal Area Network)3108 00 27 00 e4 38 VirtualBox Host-Only Ethernet Adapter
IPv4 Route TableNetwork Destination Netmask Gateway Interface Metric 0000 0000 1721711 17217168138 25 127000 255000 On-link 127001 306 127001 255255255255 On-link 127001 306 127255255255 255255255255 On-link 127001 306 16925400 25525500 On-link 16925440182 276 16925440182 255255255255 On-link 16925440182 276 169254255255 255255255255 On-link 16925440182 276 1721700 25525500 On-link 17217168138 281 17217168138 255255255255 On-link 17217168138 281 17217255255 255255255255 On-link 17217168138 281 224000 240000 On-link 16925440182 276
Useful Commands
Network Layer 4-8
(Arpexe) Displays current ARP entries by interrogating the current protocol data If inet_addr is specified the IP and Physical addresses for only the specified computer are displayed If more than one network interface uses ARP entries for each ARP table are displayed
CUsersjbgtarp -a
Interface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527252 f0-1f-af-2f-e1-27 dynamic 1302152863 00-16-3e-c5-01-25 dynamic 13021529165 00-24-e8-32-32-1d dynamic 13021531255 ff-ff-ff-ff-ff-ff static
Useful Commands
Link Layer 5-9
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Network Layer 4-6
Netstat (Netstatexe) Displays active TCP connections ports on which the computer is listening Ethernet statistics the IP routing table and IPv4IPv6 statistics
CUsersjbgtnetstat
Proto Local Address Foreign Address State TCP 1270011029 jb-laptop5354 ESTABLISHED TCP 1270011036 jb-laptop27015 ESTABLISHED TCP 1270011047 jb-laptop19872 ESTABLISHED TCP 12700139055 jb-laptop39054 ESTABLISHED TCP 172171681382492 blugro5relay2492 ESTABLISHED
CUsersjbgtnetstat -sIPv4 Statistics Packets Received = 10158258 Received Header Errors = 2848 Received Address Errors = 2192434 Datagrams Forwarded = 0 Unknown Protocols Received = 170614 Received Packets Discarded = 4173788 Received Packets Delivered = 6692404
Useful Commands
Network Layer 4-7
Network Command Shell (Netshexe) Displays or modifies the network configuration of a local or remote computer that is currently running This command-line scripting utility has a huge number of options which are fully detailed in Help
TCPIP Route (Routeexe) Displays and modifies entries in the local IP routing table
CUsersjbgtroute printInterface List1360 36 dd aa 13 65 Intel(R) Centrino(R) Wireless-N 22301260 36 dd aa 13 69 Bluetooth Device (Personal Area Network)3108 00 27 00 e4 38 VirtualBox Host-Only Ethernet Adapter
IPv4 Route TableNetwork Destination Netmask Gateway Interface Metric 0000 0000 1721711 17217168138 25 127000 255000 On-link 127001 306 127001 255255255255 On-link 127001 306 127255255255 255255255255 On-link 127001 306 16925400 25525500 On-link 16925440182 276 16925440182 255255255255 On-link 16925440182 276 169254255255 255255255255 On-link 16925440182 276 1721700 25525500 On-link 17217168138 281 17217168138 255255255255 On-link 17217168138 281 17217255255 255255255255 On-link 17217168138 281 224000 240000 On-link 16925440182 276
Useful Commands
Network Layer 4-8
(Arpexe) Displays current ARP entries by interrogating the current protocol data If inet_addr is specified the IP and Physical addresses for only the specified computer are displayed If more than one network interface uses ARP entries for each ARP table are displayed
CUsersjbgtarp -a
Interface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527252 f0-1f-af-2f-e1-27 dynamic 1302152863 00-16-3e-c5-01-25 dynamic 13021529165 00-24-e8-32-32-1d dynamic 13021531255 ff-ff-ff-ff-ff-ff static
Useful Commands
Link Layer 5-9
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Network Layer 4-7
Network Command Shell (Netshexe) Displays or modifies the network configuration of a local or remote computer that is currently running This command-line scripting utility has a huge number of options which are fully detailed in Help
TCPIP Route (Routeexe) Displays and modifies entries in the local IP routing table
CUsersjbgtroute printInterface List1360 36 dd aa 13 65 Intel(R) Centrino(R) Wireless-N 22301260 36 dd aa 13 69 Bluetooth Device (Personal Area Network)3108 00 27 00 e4 38 VirtualBox Host-Only Ethernet Adapter
IPv4 Route TableNetwork Destination Netmask Gateway Interface Metric 0000 0000 1721711 17217168138 25 127000 255000 On-link 127001 306 127001 255255255255 On-link 127001 306 127255255255 255255255255 On-link 127001 306 16925400 25525500 On-link 16925440182 276 16925440182 255255255255 On-link 16925440182 276 169254255255 255255255255 On-link 16925440182 276 1721700 25525500 On-link 17217168138 281 17217168138 255255255255 On-link 17217168138 281 17217255255 255255255255 On-link 17217168138 281 224000 240000 On-link 16925440182 276
Useful Commands
Network Layer 4-8
(Arpexe) Displays current ARP entries by interrogating the current protocol data If inet_addr is specified the IP and Physical addresses for only the specified computer are displayed If more than one network interface uses ARP entries for each ARP table are displayed
CUsersjbgtarp -a
Interface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527252 f0-1f-af-2f-e1-27 dynamic 1302152863 00-16-3e-c5-01-25 dynamic 13021529165 00-24-e8-32-32-1d dynamic 13021531255 ff-ff-ff-ff-ff-ff static
Useful Commands
Link Layer 5-9
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Network Layer 4-8
(Arpexe) Displays current ARP entries by interrogating the current protocol data If inet_addr is specified the IP and Physical addresses for only the specified computer are displayed If more than one network interface uses ARP entries for each ARP table are displayed
CUsersjbgtarp -a
Interface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527252 f0-1f-af-2f-e1-27 dynamic 1302152863 00-16-3e-c5-01-25 dynamic 13021529165 00-24-e8-32-32-1d dynamic 13021531255 ff-ff-ff-ff-ff-ff static
Useful Commands
Link Layer 5-9
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-9
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-10
Link layer introductionterminology hosts and routers
nodes communication
channels that connect adjacent nodes along communication path links wired links wireless links LANs
layer-2 packet frame encapsulates datagramdata-link layer has responsibility of
transferring datagram from one node to physically adjacent node over a link
global ISP
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-11
Link layer context datagram transferred
by different link protocols over different links eg Ethernet on
first link frame relay on intermediate links 80211 on last link
each link protocol provides different services eg may or may not
provide rdt over link
framing link access encapsulate datagram
into frame adding header trailer
channel access if shared medium
ldquoMACrdquo addresses used in frame headers to identify source dest bull different from IP
address
reliable delivery between adjacent nodeswe learned how to do this already ndash Transport layerseldom used on low bit-error link (fiber some twisted pair)wireless links high error rates
Q why both link-level and end-end reliability
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-12
flow control pacing between adjacent sending and receiving
nodes error detection
errors caused by signal attenuation noise receiver detects presence of errors
bull signals sender for retransmission or drops frame error correction
receiver identifies and corrects bit error(s) without resorting to retransmission
half-duplex and full-duplex with half duplex nodes at both ends of link can
transmit but not at same time
Link layer services (more)
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-13
Where is the link layer implemented in each and every host link layer implemented
in ldquoadaptorrdquo (aka network interface card NIC) or on a chip Ethernet card
80211 card Ethernet chipset
implements link physical layer
attaches into hostrsquos system buses
combination of hardware software firmware
controller
physicaltransmission
cpu memory
host bus (eg PCI)
network adaptercard
applicationtransportnetwork
link
linkphysical
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-14
Link layer LANs outline51 introduction services52 error detection correction SKIPPED53 multiple access protocols54 LANs
addressing ARP Ethernet switches VLANS
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-15
Multiple access links protocolstwo types of ldquolinksrdquo point-to-point NO
Collisions PPP for dial-up access point-to-point link between Ethernet switch host
broadcast (shared wire or medium) Collisions old-fashioned Ethernet upstream HFC 80211 wireless LAN algorithm that determines how nodes share
channel
shared wire (eg cabled Ethernet)
shared RF (eg 80211 WiFi)
shared RF(satellite)
humans at acocktail party
(shared air acoustical)
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-16
MAC protocols taxonomythree broad classes of sharing channel partitioning
divide channel into smaller ldquopiecesrdquo (time slots frequency code)
allocate piece to node for exclusive use Subdividing the capacity ndash TDM FDM
random access channel not divided allow collisions ldquorecoverrdquo from collisions
ldquotaking turnsrdquo nodes take turns but nodes with more to send can
take longer turns
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-17
Random access protocols when node has packet to send
transmit at full channel data rate R no a priori coordination among nodes
two or more transmitting nodes ldquocollisionrdquo
random access MAC protocol specifies how to detect collisions how to recover from collisions (eg via
delayed retransmissions) examples of random access MAC
protocols slotted ALOHA ALOHA CSMA CSMACD CSMACA
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-18
Slotted ALOHAassumptions all frames same size time divided into
equal size slots (time to transmit 1 frame)
nodes start to transmit only slot beginning
nodes are synchronized
if 2 or more nodes transmit in slot all nodes detect collision
operation when node obtains fresh
frame transmits in next slot if no collision node
can send new frame in next slot
if collision node retransmits frame in each subsequent slot with prob p until success
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-19
Pros single active node
can continuously transmit at full rate of channel
highly decentralized only slots in nodes need to be in sync
simple
Cons collisions wasting
slots idle slots nodes may be able
to detect collision in less than time to transmit packet
clock synchronization
Slotted ALOHA1 1 1 1
2
3
2 2
3 3
node 1
node 2
node 3
C C CS S SE E E
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-20
suppose N nodes with many frames to send each transmits in slot with probability p
prob that given node has success in a slot = p(1-p)N-1
prob that any node has a success = Np(1-p)N-1
max efficiency find p that maximizes Np(1-p)N-1
for many nodes take limit of Np(1-p)N-1
as N goes to infinity gives
max efficiency = 1e = 37
efficiency long-run fraction of successful slots (many nodes all with many frames to send)
at best channelused for useful transmissions 37of time
Slotted ALOHA efficiency
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-21
max efficiency find p that maximizes F(p) = Np(1-p)N-1
max efficiency when Frsquo(p) = 0dFdp = d (Np(1-p)N-1 ) dp = N(1-p)N-1 + Np(N-1)(-1)(1-p)N-2
N(1-p)N-1 = Np(N-1)(1-p)N-1 (1 ndash p) 1 = p(N ndash 1) ( 1 ndash p)( 1 ndash p ) = p ( N ndash 1) = pN - p 1 = pN p = 1 N
F(max) = N(1N)(1-(1N))N-1
= ( 1 ndash 1N ) N-1
As N goes to infinity F(max) = 1 e = 037
Slotted ALOHA efficiency
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-22
Pure (unslotted) ALOHA unslotted Aloha simpler no synchronization when frame first arrives
transmit immediately collision probability increases
frame sent at t0 collides with other frames sent in [t0-1t0+1]
Efficiency of only 018
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-23
CSMA (carrier sense multiple access)
CSMA listen before transmitif channel sensed idle transmit entire
frame if channel sensed busy defer
transmission
human analogy donrsquot interrupt others
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-24
CSMA collisions collisions can still
occur propagation delay means two nodes may not hear each otherrsquos transmission
collision entire packet transmission time wasted distance amp
propagation delay play role in determining collision probability
spatial layout of nodes
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-25
CSMACD (collision detection)CSMACD carrier sensing deferral as in
CSMA collisions detected within short time colliding transmissions aborted reducing
channel wastage collision detection
easy in wired LANs measure signal strengths compare transmitted received signals
difficult in wireless LANs received signal strength overwhelmed by local transmission strength
human analogy the polite conversationalist
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-26
CSMACD (collision detection)
spatial layout of nodes
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-27
Ethernet CSMACD algorithm1 NIC receives
datagram from network layer creates frame
2 If NIC senses channel idle starts frame transmission If NIC senses channel busy waits until channel idle then transmits
3 If NIC transmits entire frame without detecting another transmission NIC is done with frame
4 If NIC detects another transmission while transmitting aborts and sends jam signal
5 After aborting NIC enters binary (exponential) backoff after mth collision
NIC chooses K at random from 012 hellip 2m-1 NIC waits K512 bit times returns to Step 2
longer backoff interval with more collisions
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-28
CSMACD efficiency Tprop = max prop delay between 2 nodes in LAN ttrans = time to transmit max-size frame
efficiency goes to 1 as tprop goes to 0 as ttrans goes to infinity
better performance than ALOHA and simple cheap decentralized
transprop ttefficiency
511
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-29
token passing control token
passed from one node to next sequentially
token message concerns
token overhead latency single point of
failure (token)
T
data
(nothingto send)
T
ldquoTaking turnsrdquo MAC protocols
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
cable headend
CMTS
ISP
cable modemtermination system
multiple 40Mbps downstream (broadcast) channels single CMTS transmits into channels
multiple 30 Mbps upstream channels multiple access all users contend for certain
upstream channel time slots (others assigned)
Cable access network
cablemodemsplitter
hellip
hellip
Internet framesTV channels control transmitted downstream at different frequencies
upstream Internet frames TV control transmitted upstream at different frequencies in time slots
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-31
DOCSIS data over cable service interface spec
FDM over upstream downstream frequency channels
TDM upstream some slots assigned some have contention downstream MAP frame assigns upstream
slots request for upstream slots (and data)
transmitted random access (binary backoff) in selected slots
MAP frame forInterval [t1 t2]
Residences with cable modems
Downstream channel i
Upstream channel j
t1 t2
Assigned minislots containing cable modemupstream data frames
Minislots containing minislots request frames
cable headend
CMTS
Cable access network
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-32
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-33
MAC addresses and ARP 32-bit IP address
network-layer address for interface used for layer 3 (network layer) forwarding
MAC (or LAN or physical or Ethernet) address function used lsquolocallyrdquo to get frame from one
interface to another physically-connected interface (same network in IP-addressing sense)
48 bit MAC address (for most LANs) burned in NIC ROM also sometimes software settable
eg 1A-2F-BB-76-09-ADhexadecimal (base 16) notation(each ldquonumberrdquo represents 4 bits)
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-34
LAN addresses and ARPeach adapter on LAN has unique LAN address
adapter
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53
LAN(wired orwireless)
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-35
LAN addresses (more) MAC address allocation administered by
IEEE manufacturer buys portion of MAC
address space (to assure uniqueness) analogy
MAC address like Social Security Number IP address like postal address
MAC flat address portability can move LAN card from one LAN to
another IP hierarchical address not portable
address depends on IP subnet to which node is attached
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-36
ARP address resolution protocol ARP table each IP node
(host router) on LAN has table
IPMAC address mappings for some LAN nodes
lt IP address MAC address TTLgt TTL (Time To Live) time
after which address mapping will be forgotten (typically 20 min)
Question how to determineinterfacersquos MAC address knowing its IP address
1A-2F-BB-76-09-AD
58-23-D7-FA-20-B0
0C-C4-11-6F-E3-98
71-65-F7-2B-08-53 LAN
137196723
137196778
137196714
137196788
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-37
ARP address resolution protocol
Question how to determineinterfacersquos MAC address knowing its IP address
ipconfig allEthernet adapter Local Area Connection
Connection-specific DNS Suffix WPIEDU Description Realtek PCIe FE Controller Physical Address B8-CA-3A-DC-C6-2B DHCP Enabled Yes Autoconfiguration Enabled Yes IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480 Lease Obtained MondayDecember 16 2013 110643 AM Lease Expires MondayDecember 16 2013 50643 PM Default Gateway 130215241 DHCP Server 1302153918 DNS Servers 1302153218 1302153918 130215518 NetBIOS over Tcpip Enabled
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-38
ARP protocol same LAN A wants to send
datagram to B Brsquos MAC address not
in Arsquos ARP table A broadcasts ARP
query packet containing Bs IP address dest MAC address =
FF-FF-FF-FF-FF-FF all nodes on LAN
receive ARP query B receives ARP
packet replies to A with its (Bs) MAC address frame sent to Arsquos MAC
address (unicast)
A caches (saves) IP-to-MAC address pair in its ARP table until information becomes old (times out) soft state information
that times out (goes away) unless refreshed
ARP is ldquoplug-and-playrdquo nodes create their
ARP tables without intervention from net administrator
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-39
walkthrough send datagram from A to B via R focus on addressing ndash at IP (datagram) and MAC layer (frame)
assume A knows Brsquos IP address assume A knows IP address of first hop router R (how)
assume A knows Rrsquos MAC address (how)
Addressing routing to another LAN
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-40
Addressing routing to another LAN
ipconfig all Physical Address B8-CA-3A-DC-C6-2B IPv4 Address 1302152836(Preferred) Subnet Mask 2552552480
getmacPhysical Address Transport Name=================== ====================B8-CA-3A-DC-C6-2B DeviceTcpip_ Wired08-00-27-00-E4-38 DeviceTcpip_ Wireless
arp -aInterface 1302152836 --- 0x10 Internet Address Physical Address Type 130215241 00-00-5e-00-01-01 dynamic 130215242 00-23-9c-94-97-f0 dynamic 13021527230 f0-1f-af-2f-e1-3f dynamic 13021529193 04-7d-7b-b0-b1-44 dynamic
route printActive RoutesNetwork Destination Netmask Gateway Interface Metric 0000 0000 130215241 1302152836 20 127255255255 255255255255 On-link 127001 306 130215240 2552552480 On-link 1302152836 276 1302152836 255255255255 On-link 1302152836 276 13021531255 255255255255 On-link 1302152836 276
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-41
Addressing routing to another LAN
IPEthPhy
IP src 111111111111 IP dest 222222222222
A creates IP datagram with IP source A destination B A creates link-layer frame with Rs MAC address as dest
frame contains A-to-B IP datagramMAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-42
Addressing routing to another LAN
IPEthPhy
frame sent from A to R
IPEthPhy
frame received at R datagram removed passed up to IP
MAC src 74-29-9C-E8-FF-55 MAC dest E6-E9-00-17-BB-4B
IP src 111111111111 IP dest 222222222222
IP src 111111111111 IP dest 222222222222
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-43
Addressing routing to another LAN
IP src 111111111111 IP dest 222222222222
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-44
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
IPEthPhy
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
R
1A-23-F9-CD-06-9B222222222220
111111111110E6-E9-00-17-BB-4BCC-49-DE-D0-AB-7D
111111111112
11111111111174-29-9C-E8-FF-55
A22222222222249-BD-D2-C7-56-2A
22222222222188-B2-2F-54-1A-0F
B
Link Layer 5-45
Addressing routing to another LAN
R forwards datagram with IP source A destination B R creates link-layer frame with Bs MAC address as dest
frame contains A-to-B IP datagram
IP src 111111111111 IP dest 222222222222
MAC src 1A-23-F9-CD-06-9B MAC dest 49-BD-D2-C7-56-2A
IPEthPhy
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-46
Link layer LANs outline51 introduction
services52 error detection
correction 53 multiple access
protocols54 LANs
addressing ARP Ethernet switches VLANS
55 link virtualization MPLS
56 data center networking
57 a day in the life of a web request
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-47
Ethernetldquodominantrdquo wired LAN technology cheap $20 for NIC first widely used LAN technology simpler cheaper than token LANs and ATM kept up with speed race 10 Mbps ndash 10 Gbps
Metcalfersquos Ethernet sketch
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-48
Ethernet physical topology bus popular through mid 90s
all nodes in same collision domain (can collide with each other)
star prevails today active switch in center each ldquospokerdquo runs a (separate) Ethernet
protocol (nodes do not collide with each other)
switch
bus coaxial cablestar
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-49
Ethernet frame structuresending adapter encapsulates IP
datagram (or other network layer protocol packet) in Ethernet frame
preamble 7 bytes with pattern 10101010 followed
by one byte with pattern 10101011 used to synchronize receiver sender
clock rates
destaddress
sourceaddress
data (payload) CRCpreamble
type
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-50
Ethernet frame structure (more) addresses 6 byte source destination MAC
addresses if adapter receives frame with matching
destination address or with broadcast address (eg ARP packet) it passes data in frame to network layer protocol
otherwise adapter discards frame type indicates higher layer protocol
(mostly IP but others possible eg Novell IPX AppleTalk)
CRC cyclic redundancy check at receiver error detected frame is droppeddest
addresssource
addressdata
(payload) CRCpreamble
type
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-51
Ethernet unreliable connectionless connectionless no handshaking between
sending and receiving NICs unreliable receiving NIC doesnrsquot send acks
or nacks to sending NIC data in dropped frames recovered only if
initial sender uses higher layer rdt (eg TCP) otherwise dropped data lost
Ethernetrsquos MAC protocol unslotted CSMACD wth binary backoff
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
Link Layer 5-52
8023 Ethernet standards link amp physical layers
many different Ethernet standards common MAC protocol and frame format different speeds 2 Mbps 10 Mbps 100
Mbps 1Gbps 10G bps different physical layer media fiber cable
applicationtransportnetwork
linkphysical
MAC protocoland frame format
100BASE-TX
100BASE-T4
100BASE-FX100BASE-T2
100BASE-SX 100BASE-BX
fiber physical layercopper (twisterpair) physical layer
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-
The End is Near
- Slide 1
- Slide 2
- Slide 3
- Slide 4
- Slide 5
- Slide 6
- Slide 7
- Slide 8
- Link layer LANs outline
- Link layer introduction
- Link layer context
- Link layer services (more)
- Where is the link layer implemented
- Link layer LANs outline (2)
- Multiple access links protocols
- MAC protocols taxonomy
- Random access protocols
- Slotted ALOHA
- Slotted ALOHA (2)
- Slotted ALOHA efficiency
- Slotted ALOHA efficiency (2)
- Pure (unslotted) ALOHA
- CSMA (carrier sense multiple access)
- CSMA collisions
- CSMACD (collision detection)
- CSMACD (collision detection) (2)
- Ethernet CSMACD algorithm
- CSMACD efficiency
- ldquoTaking turnsrdquo MAC protocols
- Slide 30
- Slide 31
- Link layer LANs outline (3)
- MAC addresses and ARP
- LAN addresses and ARP
- LAN addresses (more)
- ARP address resolution protocol
- ARP address resolution protocol (2)
- ARP protocol same LAN
- Addressing routing to another LAN
- Addressing routing to another LAN (2)
- Addressing routing to another LAN (3)
- Addressing routing to another LAN (4)
- Addressing routing to another LAN (5)
- Addressing routing to another LAN (6)
- Addressing routing to another LAN (7)
- Link layer LANs outline (4)
- Ethernet
- Ethernet physical topology
- Ethernet frame structure
- Ethernet frame structure (more)
- Ethernet unreliable connectionless
- 8023 Ethernet standards link amp physical layers
- The End is Near
-