Download - Lect06 Ethernet
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Data Communication and
Networking
Ethernet and Wireless LAN
IEEE802 Standard for LANS
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Ethernet Evolution
IEEE802.3 Ethernet Frame
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Addressing
Each station on an Ethernet network (such as a PC,
workstation, or printer) has its own network interface card
(NIC).TheNICfitsinsidethestationandprovidesthestation
withalink-layeraddress.TheEthernetaddressis6bytes(48
bits), normally written inhexadecimalnotation, witha colon
betweenthebytes.
Implementation of standard Ethernet
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Access Method
SincethenetworkthatusesthestandardEthernetprotocolis
a broadcast network,weneed touseanaccessmethod to
controlaccesstothesharingmedium.ThestandardEthernet
choseCSMA/CDwith1-persistentmethod.
10BASE5 Implementation
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10BASE-T Implementation
Collision domains
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Switched Ethernet
Full duplex switched Ethernet
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IEEE802.3u Fast Ethernet
IEEE802.3z Gigabit Ethernet
Theneedforanevenhigherdatarateresultedinthedesign
of the Gigabit Ethernet Protocol (1000 Mbps). The IEEE
committee calls it the Standard 802.3z. The goals of the
GigabitEthernetweretoupgradethedatarateto1Gbps,but
keeptheaddresslength,theframeformat,andthemaximum
andminimumframelengththesame.
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MAC Sublayer
AmainconsiderationintheevolutionofEthernetwastokeep
the MAC sublayer untouched. However, to achieve a data
rateof1Gbps,thiswasnolongerpossible.GigabitEthernet
has two distinctive approaches for medium access: half-
duplexandfull-duplex.Almostall implementationsofGigabit
Ethernetfollowthefull-duplexapproach,sowemostlyignore
thehalf-duplexmode.
Encoding in Gigabit Ethernet
IEEE802.3ab
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Gigabit Ethernet implementations
IEEE802.3ae 10-Gigabit Ethernet
Inrecentyears,therehasbeenanotherlookintotheEthernet
for use in metropolitan areas. The idea is to extend the
technology,thedatarate,andthecoveragedistancesothat
theEthernetcanbeusedasLANandMAN,MetroEthernet
orMetroLAN.
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10-GbE implementations
IEEE802.3ba 40/100-Gigabit Ethernet
40 Gbit/s and 100 Gbit/s Ethernet. 40 Gbit/s over 1m
backplane,10 mCucableassembly(4x25Gbitor10x10Gbit
lanes) and 100 mofMMF and 100 Gbit/s up to 10 m of Cu
cableassembly,100mof MMF or40 kmof SMF respectively.
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Hierarchical Ethernet LAN
Three categories of connecting devices
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Layer 1: Hub
A hub is a device that operates only in the physical layer.
Signals that carry information within a network can travel a
fixed distance before attenuation endangers the integrity of
thedata.Arepeaterreceivesasignaland,beforeitbecomes
tooweakorcorrupted, regeneratesand retimes the original
bitpattern.
Layer2: Link-Layer Switches
A link-layerswitch (or switch) operates in both the physical
and the data-link layers. As a physical-layer device, it
regeneratesthesignalitreceives.Asalink-layerdevice,the
link-layerswitchcanchecktheMACaddresses(sourceand
destination)containedintheframe.
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Ethernet Switch
Learning switch
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Loop problem in a learning switch Part C)
Loop problem in a learning switch Part D)
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System of connected LANs and its graph Part a)
System of connected LANs and its graph Part b)
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Finding the shortest path and the spanning tree
Forwarding and blocking ports after using spanning
tree algorithm
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Layer 3: Routers and Layer3 Switch
Virtual LAN
AstationisconsideredpartofaLANifitphysicallybelongsto
that LAN. The criterion ofmembership is geographic.What
happensifweneedavirtualconnectionbetweentwostations
belonging to two different physical LANs?We can roughly
define a virtual local area network (VLAN) as a local area
networkconfiguredbysoftware,notbyphysicalwiring.
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A switch connecting three LANs
A switch using VLAN software
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Two switches in a backbone using VLAN
VLAN with Ethernet Switches
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VLAN Membership
Vendors use different characteristics such as interface
numbers, port numbers,MAC addresses, IP addresses, IP
multicast addresses, or a combination of two or more of
these.
Single Point of Failure and 802.1D
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Switch Purchasing Considerations
NumberandSpeedsofPorts
Buyersmust decide on thenumber of ports needed and
thespeedofeach
Buyers often can buy a prebuilt switch with this
configuration
Store-and-Forward Versus Cut-Through Switching
Store-and-forward switches receive the entire frame before
sendingbitsbackout
Cut-through switches send the frame out after only a few
octets
Cut-through switches reduce latency, but this is rarely
importantattodaysswitchspeeds
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Manageability
SNMPManagercontrolsmanymanagedswitches
Manageability
Polling enables managers to collect data and diagnose
problems
Switches can be fixed remotely by changing their
configurations
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Manageability
Managerprovidesthenetworkadministratorwithsummary
performancedata
Managedswitchesaresubstantiallymore expensive than
unmanagedswitches
However,inlargenetworks,thesavingsinlaborcostsand
rapid responseareworth it, reducing the TCO compared
withunmanagedswitches
Switches fit into standard
19-inchwide(48-cmwide)
equipmentracks
Switchheightsusuallyare
multiplesof1U(1.75inor
4.4cm)
Physical and Electrical Features
19 inches
(48 cm)
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Fixed-port switches
Noflexibility:Thenumberofportsisfixed
1or2Utall
Mostworkgroupswitchesarefixed-portswitches
Stackable switches
Fixednumberofports
1Uor2Utall
High-speedinterconnectbusconnectsstackedswitches
Portscanbeaddedinincrementsofasfewas12
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Modular switches
1Uor2Utall
Containoneorafewslots
Eachslotmodulecontains1to4ports
Module
SeveralUtall
Containseveralexpansion
slots
Each expansion board
containsseveralslots
Most core switches are
chassisswitches
Chassis switches
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IEEE802.3at Power Over Ethernet
Switchesrequireelectricalpower
Inaddition,switchescanprovideelectricalpowertodevices
connectedbyUTPcables
WithPoE,switchescansupply25.5WDCpowertodevices
connectedbyUTPcables
IEEE802.3az Energy-Efficient Ethernet
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Wireless LANs
Isolated LANs: wired versus wireless
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Connection of a wired LAN and a wireless LAN to
other
Access Control
Maybe the most important issue we need to discuss in a
wirelessLANisaccesscontrolhowawirelesshostcanget
accesstothesharedmedium(air).TheCSMA/CDalgorithm
doesnotworkinwirelessLANsforthreereasons:
Wireless hosts do not have enough power to send and
receiveatthesametime.
ThehiddenstationproblempreventscollisiondetectionThedistancebetweenstationscanbegreat.
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Hidden station problem
Hidden station problem
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IEEE 802.11 PROJECT
IEEEhasdefinedthespecificationsforawirelessLAN,called
IEEE802.11,whichcoversthephysicalanddata-linklayers.
It issometimes calledwirelessEthernet. Insomecountries,
including the United States, the public uses the term WiFi
(short for wireless fidelity) as a synonym for wireless LAN.
WiFi,however,isawirelessLANthatiscertifiedbytheWiFi
Alliance.
Architecture
Thestandarddefinestwokindsofservices:thebasicservice
set(BSS)andtheextendedserviceset(ESS).
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Basic service sets BSSs)
Extended service set ESS)
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MAC Sublayer
IEEE 802.11 defines two MAC sublayers: the distributed
coordination function (DCF) and point coordination function
(PCF). Next figure shows the relationship between the two
MACsublayers,theLLCsublayer,andthephysicallayer.We
discuss the physical layer implementations later in the
chapterandwillnowconcentrateontheMACsublayer.
MAC layers in IEEE 802.11 standard
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NAV
CSMA/CA and NAV
Example of repetition interval
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Frame format
Specifications
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802.11 Wireless Access Points and NICs
Bluetooth
BluetoothisawirelessLANtechnologydesignedtoconnect
devices of different functions when they are at a short
distance from each other. Bluetooth was standardized as
IEEE802.15.1, but the standard isno longermaintained.A
BluetoothLANisanadhocnetwork.Thedevices,sometimes
calledgadgets,findeachotherandmakeanetworkcalleda
piconet.
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Piconet
Scatternet
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Single-secondary communication
Multiple-secondary communication
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Other Local Wireless Technologies
UWB
ZigBee
RFIDs
NFC
Software-definedradio
RFID Radio Frequency ID) Tags
LikeUPCtagsbutreadableremotely
Inmost cases, the radio signal from the reader provides
powerfortheRFIDtag
TheRFID tag uses this power to send informationabout
itself
Battery-operated RFID tags can send farther and send
moreinformation
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Near Field Communication
Software-Defined Radio
Canimplementmultiplewirelessprotocols
Noneedtohaveseparateradiocircuitsforeachprotocol
Reducesthecostofmulti-protocoldevices
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Mobile WiMAX