internet layer model layerscs.hac.ac.il/staff/martin/networks/slide05.pdf · computer networks —...

1Dr. Martin LandInfrastructure LayersComputer Networks — Hadassah College — Fall 2015

Infrastructure

Layers


Infrastructure

Change in point of viewInternet standards do not discuss Data Link + Physical LayersHardware developers define standards

Not Internet Aware

Internet Aware

Internet Layer Model

Data Link Layer — hardware managementPhysical Layer — hardware

Infrastructure

End-to-end IP routing + forwardingNetwork

Local + remote portsService requirements

Transport

Internet application Expects Internet services from OS

Application

Internet perspective


Infrastructure layersBottom-up design

Physical layer (PHY)Defines physical transmission of bitsExploits a physical technology

Data Link layer (DL) defines management of Physical LayerHow to make physical technology do what we want

Infrastructure managementDelivering data messages — 10% of effortMaking hardware work correctly — 90% of effort

OAM = Operations+Administration+MaintenanceApplication assumes infrastructure "just works""Just works" ⇒

Reliability, availability, stability, serviceability, growth

InfrastructureEngineering perspective

physical bits


Enormous investment in existing equipmentGlobal network of hardware nodes + transmission lines

Developed to provide many servicesInternet (IP-based unreliable connectionless) just one service

Most developed before Internet Telegraph — 1794Telephone — 1876Teletype modem — 1943Digital telephone — 1962Internet opened to public — 1992

Hardware updates Replacement of manufactured hardwareSlower than software updatesMore expensive than software updates

InfrastructureEconomic perspective


Data Link FunctionsSimilar to transport layer functions

FramingAssemble network PDUs into hardware packetsAttach header + trailer for Data Link and Physical layers

Medium access + flow control + congestion control When / how transmitter sends data onto linkTransmitter avoids overflow of receiver bufferTransmitters avoid interfering with other transmitters

Error controlDetect / correct transmission bit errors

Local addressingConvert network addresses to hardware local addresses

Transport Reliability

Data LinkReliability

Data LinkReliability


Data Link SublayersLogical Link Control (LLC) sublayer

Multiplexing of data sources / destinationsPacket type identificationError correctionFlow control

Medium Access (MAC) sublayerNetwork topologyMedium access management

Sharing medium among nodesPermission to transmit

Data frame structureHardware (MAC) addressingError detection

1

2MAC

Sublayer

Physical Layer

Data Link Layer

LLC Sublayer


Interface to Data Link LayerInfrastructure layers

Typically implemented in hardware PHY — physical circuits for transmitter / link / receiverDL — embedded program in firmware (ROM) + controller

Host nodeNetwork interface Card (NIC)

Connection port to medium (link)ControllerTransceiver

Switching nodeSwitching fabricController + multiple transceivers + connection ports to medium (link)

DL layer interfaceInterface to OS level hardware driverNetwork PDU ↔ OS driver ↔ NIC / switch controller ↔ transceiver


FramingData frame format

Data link protocol managementHeader / Trailer format

Similar to headers at network and transport layersAddressing, error control, flow control, …

Physical layer hardware managementTransmission parameters

Bit rate, Baud rate, modulation method, …Transmitter / receiver synchronization

Clock training bits1010101010 … allows receiver clock to sync

Frame markingStart / Stop Fields Start field / byte countLose sync ⇒ drop frame + wait for new Start Field

TrailerDataHeader


Frame Marking MethodsSTX / ETX

ASCII control codes

DLE in data streamByte stuffingTransmitter sends DLE as DLE DLEReceiver removes extra DLE

0x10Data Link EscapeDLE0x03End of TextETX0x02Start of TextSTX

DLE ETXRest of TrailerData Rest of HeaderDLE STX


Frame Marking MethodsFlags

Start = Stop = 01111110 = 0x7E

7E in data streamByte / bit stuffingByte stuffing

Send 7E as 7E 7E — receiver removes extra 7EBit stuffing

Send 11111 as 111110 — receiver removes extra 0

01111110Rest of TrailerData Rest of Header01111110


Error ControlCheck sequence

Transmitter Calculates hash of data Includes sequence in transmitted header / trailer

Receiver Calculates hash of data Compares received sequence with calculated sequence


Error ControlParity (even parity)

Parity bit = XOR of data bits Data + parity = even number of 1 bits

Cyclic Redundancy Code (CRC)D = Data fieldG = Generator

Predetermined pattern of r+1 bits

R = Remainder of (D × 2r) / G (modulo 2 division) = CRC fieldGenerally (D × 2r + R) / G = 0

R = (D × 2r) / GD = data


Modulo 2 Polynomial ArithmeticRepresent data bits as coefficients of polynomial

Arithmetic modulo 2 in each order (XOR)

Polynomial addition = subtraction

Polynomial multiplication / divisionMultiply / divide as usualModulo 2 arithmetic in each orderExamples

( )1 2 0

1 2 01 2 0

...

...n n

n nn n

D a a aD x a x a x a x

− −

− −− −

=

= × + × + ×

( ) ( ) ( )( ) ( )

1 0 1 01 0 1 0

1 01 1 0 0

... ...

...

n nn n

nn n

A x B x a x a x b x b x

a b x a b x

− −− −

−− −

± = × + + × ± × + + ×

= ⊕ × + + ⊕ ×

0 0 1 1 0 0 1 1 0 1+ = + = + = + =

( )( ) ( )

( ) ( )

3 2 5 3 3 5 3 5

5 2 3

1 1 1

1

x x x x x x x x x x x x

x x x x x

+ + = + + + = + + + = +

+ ÷ + = +14Dr. Martin LandInfrastructure LayersComputer Networks — Hadassah College — Fall 2015

Modulo 2 Long Division

5

2

2 5

3

5 3

3

3

1

1

0

x xx

x x xx

x x

x xx

x

x

++

++

++

++


Cyclic Redundancy Code (CRC)Why it works

Data

Shift left D r bits ⇒ D → D × 2r

Divide by G ⇒ D × 2r → D × 2r / G = Q + R / GQuotient QRemainder R

Transmit T = D × 2r + R

Receiver calculates T / GT / G = D × 2r / G + R / G = (Q + R / G) + R / G = Q + (R + R) / G

= Q + 0 / G = Q

D = data

0 … 0D = data

RD = data


CRC ExampleData stream

D = 1101011011Generator

G = 10011

Remainder R = 1110

TransmitT = 1101011011 1110

CRC check at receiver

1 1 0 0 0 0 1 0 1 0 1 0 0 1 1 1 1 0 1 0 1 1 0 1 1 0 0 0 0 1 0 0 1 1 1 0 0 1 1 1 0 0 1 1 0 1 0 1 1 0 1 0 0 1 1 0 0 1 0 1 0 0 1 0 0 1 1 1 1 1 0

1 1 0 0 0 0 1 0 1 0 1 0 0 1 1 1 1 0 1 0 1 1 0 1 1 1 1 1 0 1 0 0 1 1 1 0 0 1 1 1 0 0 1 1 0 1 0 1 1 1 1 0 0 1 1 0 0 1 0 0 1 1 1 0 0 1 1 Zero remainder ⇒ no error 0 0


CRC Standards

12 11 3 2 1

16 15 2

16 15 5

32 26 23 22 16 12 11 10 8 7 5 4 2

( ) 1

( ) 1

( ) 1

( ) 1

CRC‐12

CRC‐16

CRC‐CCITT

CRC‐32

G x x x x x x

G x x x x

G x x x x

G x x x x x x x x x x x x x x x

= + + + + +

= + + +

= + + +

= + + + + + + + + + + + + + +


Flow ControlGo Back N (GBN)

Transmit N frames Wait for ACKPiggybacking — transmit ACK signals in data frame

Sliding WindowN-bit SEQ numberWindow size — number of unACKed frames before stoppingSource window

SEQ numbers of unACKed framesFrames buffered at transmitter until ACKed

Destination windowSEQ numbers of frames to be acceptedFrames passed to network layer in SEQ order

Out-of-order frames bufferedFrames too far ahead of window rejected

Timeout — retransmit if no ACK after fixed time


High‐Level Data Link Control (HDLC)Family of data link protocols

Based on IBM SDLC Layer 2 protocol in mainframe SNA Originally for communication between CPUs and peripherals

Link Access Protocol (LAP)Versions of HDLC used in public network architectures

SLIP, PPPInternet point‐to‐point

IEEE 802.2Ethernet Logical Link Control (LLC)

LAPDISDN

LAPFFrame Relay

LAPBX.25


High‐Level Data Link Control (HDLC)Data link attributes in HDLC

Information, Supervisory, UnnumberedFrame types

3‐bit SEQ numberFlow control

16‐bit CRC‐CCITT or 32‐bit CRC‐32Error control

hardware level addressing possibleAddressing

0x7E flag with byte / bit stuffingFraming


HDLC Frame StructureGeneral HDLC frame

Address8 bit address ⇒ 256 hardware addresses

Control fieldSpecifies frame type / control

01111110 Address Control data CRC 01111110

8 8 8 ≥ 0 16 / 32 8

7 6 5 4 3 2 1 0

Information (data) 0 SEQ N(S) p/f NEXT N(R)

7 6 5 4 3 2 1 0

Supervisory (flow control) 1 0 type p/f NEXT N(R)

7 6 5 4 3 2 1 0

Unnumbered (management / connectionless) 1 1 type p/f subtype


HDLC Control FieldsFlow control

SEQ — sequence number of data frameNEXT — next expected SEQ (ACK all previous frames)

Type00 — ACK + Receiver Ready (RR)01 — Reject (REJ): retransmit all frames from N(R) 10 — Receiver Not Ready (RNR): ACK N(R) but stop sending11 — Selective Reject (SREJ): retransmit N(R)

7 6 5 4 3 2 1 0


7 6 5 4 3 2 1 0


7 6 5 4 3 2 1 0



HDLC PollingPolling

Primary host initiates communicationSecondary host responds

Poll / Final (p/f) bitInvitation — primary to secondary with p = 1Response

Secondary sends I-frames to primary with f = 0Secondary sets f = 1 on last response frame

7 6 5 4 3 2 1 0


7 6 5 4 3 2 1 0


7 6 5 4 3 2 1 0



HDLC Internet Dial‐Up ProtocolsSerial Line Internet Protocol (SLIP)

RFC 1055

Point-to-Point Protocol (PPP)Layer 2 protocol used between

Internet routersHost and Internet service provider (ISP)

Address = 11111111 = broadcastHDLC control = 11000000 = Unnumbered (connectionless data)Protocol

Protocol in data fieldNetwork protocol or link negotiation protocol (upper layer 2 sublayer)

0xC0IP datagram with byte stuffing (C0 → DB DC, DB→ DB DB)0xC0

01111110 11111111 11000000 Protocol Data CRC 01111110 8 8 8 8 or 16 ≥ 0 16 / 32 8


PPP Protocol OptionsStandard network protocols

IP, IPX, AppleTalk, …Datagram in data field

Control ProtocolsLink Control Protocol (LCP)

PPP optionsHeader compression (remove control / address fields)Size of protocol / CRC fields and data

Test Terminate

Network Control Protocol (NCP)Network layer options

ProtocolAddressHeader compression (encode header fields)

Authentication (ISP user / password exchange)

01111110 11111111 11000000 Protocol Data CRC 01111110 8 8 8 8 or 16 ≥ 0 16 / 32 8


Shared Medium NetworksPhysical layer

Multiple nodes transmit on single mediumTime divisionFrequency divisionCode division

Shared physical medium ⇒ local area network (LAN)

Data link layerMedium access (MAC) sublayer

Allocates medium capacity among nodesError detectionNetwork topology

Logical link control (LLC) sublayerFrame typesFlow controlError correctionProtocol negotiation

1

2MAC

Sublayer

Physical Layer

Data Link Layer

LLC Sublayer


Medium Access SharingTime division

Each host granted full bandwidth in allocated time slotTime slot allocated statistically or deterministically

ExamplesDeterministic — telephone switchingStatistical — Ethernet, WiFi, …

Frequency divisionEach host granted partial bandwidth in all time slotsExamples

Commercial radio / TVBluetooth

Code divisionEach host granted full bandwidth in all time slotsEach host transmits using different coding schemeExample

Cellular CDMA28Dr. Martin LandInfrastructure LayersComputer Networks — Hadassah College — Fall 2015

Common Shared Medium Networks

ITU 2G / 3G cellular network

Wireless code‐division accessCDMA / CDMA2000

ITU 2G / 3G cellular network

Wireless time/frequency‐division accessGSM / UTMS

IEEE 802.16 metropolitan area network

Wireless time/frequency‐division accessWiMAX

IEEE 802.15 personal area network

Wireless frequency‐division accessBluetooth

IEEE 802.11 local area network

Wireless time‐division access

IEEE 802.3 local area network

Wired time‐division access

WiFi

Ethernet


What are IEEE 802 and ITU?Institute of Electrical and Electronics Engineers (IEEE)

Professional organization Coordinates technical standards for electronic equipment

IEEE 802 CommitteeStandards committee for Data Link and Physical LayerOEMs (original equipment manufacturers)

Develop hardware / software systems at infrastructure layersRequest standardization (recognition) from 802 committee

Other 802 standards802.1 — bridging (interconnecting different 802 LANs)802.2 — LLC sublayer for 802 LANs802.4 — Token Bus (LAN for manufacturing environments)802.5 — Token Ring (ring topology LAN)

International Telecommunication Union (ITU)UN standards committee Sets telephone and (non-Internet) WAN standards


Time Division Medium Access Deterministic

PollingPrimary node initiates session (sends data to secondary)Secondary node responds (sends data to primary)Optional mode in WiFi

Token passingToken message passes from host to hostHost with token may transmit Token Ring, Token Bus, FDDI

Statistical Aloha

Hosts transmit at random / hope to avoid collisions

Carrier senseHosts listen for other transmissions / try to avoid collisions

ArbitrationDeterministic procedure chooses among random group of hosts

token

1 2


ALOHAnetBackground

First wireless packet data network (1971)Low data volume Connected University of Hawaii campuses (separate islands)

Protocol Host transmits when readyTwo frames overlap in time

Collision ⇒ both frames corruptedRetransmit after random wait

time

Node1234

t1 t2 t3 t4

collisions


Utilization and Throughput

0

1time (seconds) to transmit 1 packet

maximum packets/second on medium =

actual packets/second transmitted by hosts

probability success (packet trans

R

GR

P

τ =

=τ

λ =

λ= = λτ

=

Capacity

Traffic

Utilization

Collisions

0

00

'

'

mitted without collision)

uncorrupted packets/secondP

PS GPR R

λ = λ =

λλ= = =

At receiver

Throughput


ALOHA ThroughputSuccess = no collisions

Previous packet starts at t2 < t3 – τNext packet starts at t4 > t3 + τInterval of no transmissions = t4 – t2 > 2τ

Packets obey Poisson statistics

time

Node1234

t1 t2 t3 t4

collisions

( ) ( ) ( )02 2 2

0

2! 0!

packets in secondsk

T GTP k T e P e e e

k−λ − τλ − τλ −λ τλ

= ⇒ = = =

S

G0.5

0.1842GS Ge−=


Slotted ALOHA Central clock

Synchronize packet transmissionsTransmit new packet constructed between tk and tk + τ

CollisionTwo nodes construct packets in same interval

Probability of success (of my packet)No other packets constructed during interval τ

( )0

0 0! G GP e e e S Ge−τλ −τλ − −τλ

= = = ⇒ =

S

G1.0

0.368


Carrier SenseCarrier Sense Multiple Access (CSMA)

Nodes listen for transmissions before transmittingNo transmission — node can transmitTransmission — node waits until end of transmission

Collision Multiple nodes transmit "at same time""Same time"

|t1 – t2| < Tpropagation

Collision Detection (CD)Nodes listen for collision

Corrupted data

On collisionAll nodes stop transmittingNodes jam transmissionNodes waits random backoff before retransmitting

Tpropagation

t1

t2


CSMA/CD Throughput

Tanenbaum, Fig. 4‐4

Persistent CSMANo carrier detected ⇒ node with data transmits

q-persistenceNode transmits with probability 0 < q < 1q < 1 ⇒ fewer collisions but longer latency


Arbitration Deterministic medium access

Random group of nodes request accessOne node chosen by deterministic algorithm No collisionsEfficient throughput

Used within computer Peripheral Component Interconnect (PCI)

Multiple CPUs and peripherals compete for access to memoryPCI bridge allocates memory access efficiently

Intel Multibus IIMultiple nodes request bus access using pseudo-randomized IDHighest ID proceeds

Binary countdown switchMultiple hosts begin transmitting onto bus

Bus output = logical OR of all inputs

Host sends 0 but sees 1 on bus ⇒ host stops 38Dr. Martin LandInfrastructure LayersComputer Networks — Hadassah College — Fall 2015

Ethernet Family of wired LAN systems

Defined at physical and data link layers Dominant / generic LAN technology

BackgroundDeveloped 1974 at Xerox PARCCommercialized by Xerox / Intel / Digital in 1980Standardized as IEEE 802.3 in 1982

10 Mb/s baseband transmissionBus topology — single coaxial cable < 2.5 kmCSMA/CD

Shared bus topology → CSMALong propagation delay on coaxial cable → CD

DevelopmentsBit rates: 10 Mbps → 100 Mbps → 1 Gbps → 10 Gbps → 100 Gbps Media: coaxial cable → hub (virtual bus on star) → switch

Ethernet switch — non-blocking N × N switch with no collisions


Ethernet Topologies

Distributed CSMA/CD1980 – 1990 Original Ethernet design at 10 Mbps

Shared physical busCoaxial cable < 2.5 km

Coaxial cable

Tpropagation

t1

t2

( ) ( )

‐65

‐6

2.5 kmEnd‐to‐end propagation delay 8 10 sec

3 10 km/sec

Bits transmitted before carrier detect 10 Mb/s 8 10 sec 80 bits

= = ××

= × × =


Ethernet Topologies

Centralized CSMA/CD1990 – presentFast Ethernet100 Mbps

Logical bus on physical starCentral hubMultiple cables < 100 mEach station (STA = node) receives logical OR of all inputsMultiple frames ⇒ collision

Passive hub

( ) ( )

‐78

‐7

200 mEnd‐to‐end propagation delay 7 10 sec

3 10 m/sec

Bits transmitted before carrier detect 100 Mb/s 7 10 sec 70 bits

= ≈ ××

= × × =


Ethernet Topologies

Ethernet switch1995 – presentPhysical star100 Mbps → 1 Gbps → 10 Gbps → 100 GbpsFast N × N non-blocking switch

Hub learns MAC addresses at each switch portEach frame directed to port by destination address in frameLarge output buffer at each port

All stations can send at same timeNo collisions

Active hub


802.3 Ethernet Standards

1 Gb/s full duplex on 2 optical fibers

1000 Base SX1000 Base LX1000 Base BX1000 Base ZX

1 Gb/s full duplex on 2 twisted pairs1000 Base TX

100 Mb/s full duplex on 2 twisted pairs100 Base TX

100 Mb/s on 1 twisted pair100 Base T

100 Mb/s full duplex on optical fibers

100 Base FX100 Base SX100 Base BX100 Base LX

10 Mb/s on 1 twisted pair10 Base T

10 Mb/s on thin coaxial cable10 Base 2

10 Mb/s on thick coaxial cable10 Base 5


Ethernet Frame

4 bytes46 – 1500 bytes2 bytes6 bytes6 bytes1 byte7 bytes

CRCDataType or Length

Src Address

Dest Address

StartPreamble

IP = 0x0800

AppleTalk = 0x809B

ARP = 0x0806

Length of data field (<1500)Length

CRC‐32CRC

Code identifying protocol in data field

Used in most Ethernet systems

Type codes > 1536 =0x600

Type

Hardware (MAC) address of node

48‐bit MAC addresses assigned by OEM and fixed in hardware

Broadcast address FF:FF:FF:FF:FF:FF (frame read by all STAs)

Address

10101011Start

7 bytes of 10101010 for sync of receiversPreamble


IEEE 802.2LLC sublayer for 802.3 Ethernet

Based on HDLCPermits connection oriented services at data link layer

802.2 I/S DSAP SSAP control data + pad

1 byte 1 byte 2 bytes 42 ‐ 1496 bytes

802.2 U DSAP SSAP control data + pad

1 byte 1 byte 1 bytes 43 ‐ 1497 bytes

Frame type + SEQ + ACK (I / S frames)

Frame type (U frame)Control

Source service access point (protocol / service at source)SSAP

Destination service access point (protocol / service at destination)DSAP


Segmentation Ethernet bridge

2-port switchConnects 2 Ethernet segmentsReduces traffic in each segment

Initialization — promiscuous modeBridge passes every Ethernet frame

Listens as destination STARepeats Ethernet frame as source STA

Bridge learns network topologyBuilds table of source MAC addressesForwards only inter-segment frames

Ethernet LAN #1

Ethernet LAN #2

Bridge


Relationship of Protocol LayersTypical network

Application Application 16‐bit

TCP Port

16‐bit TCP Port

32‐bit IP Address

32‐bit

IP Address 32‐bit

IP Address

32‐bit IP Address

32‐bit IP Address

32‐bit

IP Address 48‐bit

Ethernet Address

48‐bit

Ethernet Address

PPP PPP 48‐bit

Ethernet Address

48‐bit

Ethernet Address

Ethernet (PHY)

Ethernet (PHY)

PHY PHY Ethernet (PHY)

Ethernet (PHY)

Host Router Router Host

Locate router by IP address(uses default gateway)

Send to router by MAC addressEthernet always uses source / destination Ethernet addresses — not IP addresses

How does host find MAC address for router?

Point‐to‐point Locate host by IP addressSend to host by MAC address


Address Resolution Protocol (ARP)Look-up MAC address by IP address (RFC 826)

Q: Who has IP = a.b.c.d ? (MAC layer broadcast)A: I am IP = a.b.c.d with MAC = u:v:w:x:y:z STAs store mappings in arp tableWindows / Linux arp –a prints arp table

ARP packet fields

Target protocol addressTPA

Target hardware address (ignored in requests)THA

Sender protocol addressSPA

Sender hardware addressSHA

1= request / 2 = replyOperation

Protocol length — length in octets of network addressPLEN

Hardware length — length in octets of MAC addressHLEN

Protocol type — network protocolPTYPE

Hardware type —MAC protocolHTYPE


Example

STA‐1IP 207.2.45.7MAC 00:cd:ef:34:54:ab

Router‐AIP 207.2.45.1MAC ab:65:46:ad:98:fe

Router‐BIP 98.57.36.1MAC ab:65:46:54:23:12

STA‐2IP 98.57.36.32MAC 00:de:87:34:e5:b3

3

2

1

CRCTCP segmentSRC: 207.2.45.7

DST: 98.75.36.32

SRC: ab:65:46:54:23:12

DST: 00:de:87:34:e5:b3


DST: 98.75.36.32PPP

MAC Trailer

IP dataIP HeaderMAC Header


DST: 98.75.36.32

SRC: 00:cd:ef:34:54:ab

DST: ab:65:46:ad:98:fe

Frames between STA‐1 and STA‐2

1

2

3


Advanced Switch / Router Interactions

Switch organizes STAs into LANIntra-LAN traffic

STAs use IP addresses as names for TCP/IP applicationsSTAs use ARP to translate IP to MAC addressSTAs send frames on LAN by MAC addressPackets contain MAC and IP address of local destination

Router organizes LAN into Internet ASInter-LAN traffic

STAs use IP addresses as names for TCP/IP applicationsLocal MAC addresses not available for remote STAs

STAs send frames via routerPackets contain

MAC address of router IP address of remote destination

Standard model



Standard subnetsubnet-1 and subnet-2 are LAN broadcast domains

Virtual LAN (VLAN)LAN switch configured to partition nodes into subnetsNo router needed for subnetting

Router Network

Subnet Subnet

Programmable Switch

Virtual LAN



Virtual Private Network (VPN)Private network implemented on public infrastructureAccess to private networks restricted by IPPossible encryption of data over public infrastructure

Internet

Private Network Private Network

Access Restricted by IP

Virtual Private Network



Standard IP model

Layer 3 switchingSwitched data link among routers

Connection-oriented virtual circuit networkFrame Relay, ATM, label switching, …

Traffic crosses router network at layer 2Saves time of layer 3 processingDatagram read / write, routing, TTLUsed for media streaming

Layer 3 Switching

Application TCP IP DL PHY

IP DL PHY


IP DL PHY

IP DL PHY

IP DL PHY


DL PHY


DL PHY

DL PHY

DL PHY



Multiprotocol Label Switching (MPLS)

Header fieldsOne or more headers per frame — "stack" of labels

Connection-orientedSet (reserve) router path before data traffic beginsLabel Distribution Protocol (LDP)RSVP-TE — extension of Resource Reservation Protocol (RSVP)

MPLS-aware routersForward frames on preset route by label ID

Label switching

Data MAC trailerTCP HeaderIP HeaderMPLSMAC Header

8‐bit time to live fieldTTL1‐bit — if set, current label is last of "stack" of labels for frameStack flag3‐bit QoS (quality of service) fieldTraffic Class20‐bit IDLabel


Tunneling in the OSI Model

NetworkLayer

(translation)

Data LinkLayer

(translation)

PhysicalLayer

(translation)

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

Local PhysicalProtocol

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

End-to-End Application Protocol

End-to-End Presentation Protocol

End-to-End Session Protocol

End-to-End Transport Protocol

Local NetworkProtocol

Local Data LinkProtocol


End User Intermediate System

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

Local SessionProtocol

Local TransportProtocol



Host / Server

PhysicalLayer



PhysicalLayer

(translation)

Proxy / Gateway

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer


Local SessionProtocol

Local TransportProtocol




Small Office / Home Office (SOHO)LAN (Local Area Network) to WAN (Wide Area Network)

Ethernet

WiFi

ADSL

WiFi Access PointEthernet Switch

IP RouterADSL Modem

Cable‐based transmission protocol defined at PHY layerG.992.5ADSL

802.11

802.3

Wireless LAN protocol defined at DATA LINK and PHY layersWiFi

Cable‐based LAN protocol defined at DATA LINK and PHY layersEthernet

Internet


Laptop Browser to Web Server — Simplified View

Access

IP

ADSL

WiFi Router

WiFi

IP

ADSL

Access

IP

ServerInternetLaptop

PHYPHY

Data LinkData LinkWiFi

IPIPIP

TCPTCP

HTTPHTTP


ADSL — Asymmetric Digital Subscriber LineHigh speed transmission on standard voice line

POTS — plain old telephone service24 Mbps downstream3.3 Mbps upstream

Ref: JDSU, ADSL Technology, JDS Uniphase Corporation, 2005


ADSL Access Network

Ref: Vodaphone, Wholesale Layer2 DSL (W‐DSL‐L2I), VTCW011 ‐ I 03/13


Typical Bezeq ATU‐R

ADSL

33 MbpsIP

Routing802.3

Ethernet802.11WiFi


Fast Internet Access

usermanagement

and IP datagramforwarding

IP datagramforwarding

Bezeq ISP

Internet routing

ADSL modem onpoint-to-point

channel

Server

IPnetwork

telephonenetwork

Client

switchedATM

network


Fast Internet Protocols — Typical Campus CasePPP

Point to Point Protocol

Logon + connection management

PPPoE

PPP over Ethernet

Virtual point‐to‐point connection over shared LAN

Client opens private session with ISP

Client

Ethernet

802.3

PPPoE

PPP

IP

TCP

App

Router

802.3

PPPoE

PPP


Fast Internet Protocols — Typical Campus CaseATM

Asynchronous Transfer Mode

Data Link protocol for broadband telephone services

Permits real time QoS

MPOA + AAL5

Adaptation protocols for ATM

ADSL

Physical bit transmission

Client

Ethernet

802.3

PPPoE

PPP

IP

TCP

App

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

Router

802.3

PPPoE

PPP

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

Bezeq


Fast Internet Protocols — Typical Campus Case

Connection to ISP

Client runs Network Control Protocol (NCP) over PPP

CHAP (challenge handshake authentication protocol) —User Name + Password

ISP authorizes user and engages IP forwarding

Client

Ethernet

802.3

PPPoE

PPP

IP

TCP

App

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

Router

802.3

PPPoE

PPP

802.3802.3

PHY

PPPoE

ADSL

ATM

AAL5

MPOA

PPPoE

Bezeq

802.3

PHY

PPPoE

PPP

ISP

Connection to ISP


Fast Internet Protocols — Typical Campus Case

IP forwarding

ISP forwards IP datagrams to server via Internet backbone

Client

Ethernet

802.3

PPPoE

PPP

IP

TCP

App

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

Router

802.3

PPPoE

PPP

802.3802.3

PHY

PPPoE

ADSL

ATM

AAL5

MPOA

PPPoE

Bezeq

802.3

PHY

PPP

IP

PHY

PPPoE

PPP

ISP

PHY

Server

PPP

IP

TCP

App

Connection to ISP

IP Routing


Fast Internet Protocols — Typical SOHO Case

Router/modem initiates connection to ISP

Runs NCP over PPP over PPPoE over Ethernet

Router provides always‐on Internet access over WiFi + Ethernet

Client

WiFi

802.11

IP

TCP

App

802.3

ADSL

ATM

AAL5

MPOA

PPPoE

PPP

Router

WiFi

802.3802.3

PHY

PPPoE

ADSL

ATM

AAL5

MPOA

PPPoE

Bezeq

802.3

PHY

PPP

IP

PHY

PPPoE

PPP

ISP

PHY

Server

PPP

IP

TCP

App

Connection to ISP

IP Routing

internet layer model layerscs.hac.ac.il/staff/martin/networks/slide05.pdf · computer networks —...

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