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Chapter 12. The IEEE LAN/MAN Committee Networking Standards

Chapter 12. The IEEE LAN/MAN Committee Networking Standards

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electricitytoyourhousetoconsumerelectronics.In

thischapteronlytheimportantnetworkingprotocols

arediscussed.FormoreinformationabouttheIEEE

andthevastrangeofactivitiesitsupports,visitits

Webpageatwww.ieee.org.



Atthetimeofthiswriting,therearealmost900standards

created(orrefined)bytheIEEEthatareinwidespreaduse.

Approximately700othersareindevelopment.Notethat

althoughtheIEEEisresponsibleforcreatingsomestandards

fromscratch,thisorganizationhasalsobeenresponsiblefor

standardizingtechnologythatwasdevelopedbyother

manufacturers.Bytakinginputfromexistingdefactostandards

andcastingthetechnologyinprint,theIEEEbenefitsboth

manufacturersandendusersalike.

Severalstepsaretakentocreateastandard(orsetof

standards)withintheIEEE:

ProjectAuthorizationRequest(PAR)ThePARisthe

beginningofthestandardizationprocess.Itdefinesthe

scopeofthenewstandardaswellasitspurposeand

contactsforindividualswhowillberesponsibleforthe

standard.Thereisanonlineformthatcanbeusedtobegin

theprocessthatstatestheproposednameofthedraft

documentaswellasthetypeofprojectandcontact

information.Asponsor(whichcanbeanindividualoran

organization)issetforthinthePAR.

CreatingaDraftUsingtemplatesprovidedbytheIEEE,a

draftofthestandardisfirstcreated.Thisdraftisthen

submittedtoaballotingprocessinwhichinputissolicitedto

makechangestoorapprovethedraftdocument.Thedraft



isthensubmittedtotheIEEE-SAStandardsBoard,which

reviewsthedocumentationandthenpublishesitforreview

byothers.Notethatadraftisjustthatitisnotafinal

standard.Itisjustthefirstiterationofthestandards

process.

StandardsThenextstepistosubmitthedocumenttothe

IEEEStandardsDepartmentforapproval.Theprocedures

involvedinthissteparemany,anditcantakesometime

beforethestandardisofficiallyapproved.Forexample,the

IEEEmaysendanapplicationtotheAmericanNational

StandardsInstitute(ANSI)foritsapproval.

PublicationAfterthestandardhasgonethroughthese

processes,itispublishedasastandardsothat

manufacturers(andotherinterestedparties)canbegin

usingit.

Thisisjustageneralexplanationofthestandardsapproval

process.Infact,therearemanyformstobefilledout,many

conditionsthatmustbemet.Theprocessinvolvesmeetingsof

theworkinggroupandconstantfeedbacktogatherthe

informationfromthevariouspartiestoensurethatthefinal

standardisaworkabledocument.Theimportantthingto

rememberfromthisisthatstandardsarenotcreatedbyjusta

singlepersonormanufacturer.Instead,theproposeddraftsare

subjecttointensescrutiny,andallaspectsofthedraftcanbe

subjecttomodificationbeforeafinalstandardisproduced.Asif

thatwerenotenough,itiscommontoseemanyestablished

standardsmodifiedtokeepupwiththeever-changingworldof

technologytoday.







WhatIstheLAN/MANCommittee?

Thischapterdiscussestheimportantstandardsasdefinedby

theLocalAreaNetwork/MetropolitanAreaNetwork(LAN/MAN)

StandardsCommittee(LMSC).Thiscommitteeconsistsof

variousworkinggroups,eachofwhichisdevotedtoaparticular

technology.Forexample,onecommitteewasresponsiblefor

thebasicEthernetstandard,andanotherwasinchargeof

developingthestandardforthefirstToken-Ringnetworks.Asif

thisdivisionwerenotenough,thereareotherworkinggroups

thatfurtherdividetheresponsibilityforaparticulartechnology.

Forexample,thereareseveralworkinggroupsactivelyworking

onwirelessstandardsatthistime.

Thefocusofthe802.*workinggroupsistrainedatthetwo

lowestlayersoftheOSIReferenceModelthephysicalanddata

linklayersandsomeaspectsofhigherlayersrelatingtonetwork

management.TheLMSCalsocoordinatesitsactivitieswith

otherstandardsbodies,suchastheInternationalOrganization

forStandardization(ISO),andotherstandardsgroupsoutside

oftheU.S.

TheOSIReferenceModelisdiscussedinAppendixA,"Overviewof

theOSISeven-LayerNetworkingReferenceModel."



Thefollowingsectionscoverimportantstandards,someof

whicharementionedforhistoricalpurposes,aswellasnewer

standardsthatarestillunderdevelopment.



IEEE802:OverviewandArchitecture



TheIEEE802standardsdocumentsetsforththegroundwork

fortheothersthatfollow.Itincludesshortdescriptionsofthe

typesofnetworksthatweretobeconsideredbythecommittee,

andareferencemodelfortheirdevelopment.ThetermsLAN

andMANaredefinedinthisdocument:

LANAlocalareanetworkistypicallypartofasingle

organization.TheLANisapeer-to-peernetworkthatallows

nodesonthenetworktocommunicatewithoneormore

nodesonthesameLAN.Intheoriginalspecification,the

bustopologywasused,thoughthedocumenthasbeen

updatedtoincludeswitchingandothermodernLAN

techniques.

MANAmetropolitanareanetworkisacollectionof

interconnectedLANsthatspanalargergeographicalarea,

suchasacampusnetworkoracity.MANscanalsobe

ownedandmaintainedbyasingleentity,butaremore

likelyofferedasservicestomultipleclientsinorderto

provideahigh-bandwidthconnectiontomultipleclient

networks.

ItisimportanttoknowthattheOSImodelisjustthat:a

model.Veryfewprotocolsactuallyadherestrictlytothismodel.

Forexample,TCP/IPwasbeingdevelopedbeforetheOSImodel

wascreated,andthustheTCP/IPmodeldiffersfromtheOSI

model.

Today,theOSIDataLinklayer,formostnetworkprotocols,is

usuallydividedintotwosublayers.TheLogicalLinkControl

(LLC)andMediaAccessControl(MAC)sublayersaretheresult

ofthisseparationofthesingleOSIDataLinklayerintotwo

components(althoughinsomestandardsthefunctionality

providedbythesesublayersbecomesalittleblurred).



TheMediaAccessControlSublayer



TheMediaAccessControlsublayerprovidesaservicetotheLLC

sublayerstogetthedatapacketsdeliveredtothedestination

node.Atthissublayerthedatatobetransmittedarereferredto

as"frames."TheMACsublayercreatestheframestobe

transmittedonthephysicalnetworkmedia,andincludessome

errorcheckingtoallowthereceivingnodetochecktheintegrity

ofthedataframe.TheMACaddressisanimportantconcept

whenusedinmodernEthernetnetworks.Asyouwilllearnin

Chapter24,"OverviewoftheTCP/IPProtocolSuite,"theIP

protocolenablesthehierarchicaladdressspacethatisusedon

WANsandtheInternet.AttheLANlevelaflataddressspaceis

usedforcommunicationsbetweennodesonthesameLAN.

ThereisanimportantdistinctiontobemadebetweenMACand

IPaddresses.MACaddressesaresimplyaddressesthatare

burnedintoanetworkcardorotherhardwarebythe

manufacturer.Partoftheaddressrepresentsthemanufacturer,

andtheremainingportionoftheaddressisassignedinaserial

fashiontoeachnetworkcardthatthemanufacturerproduces.

Becausethereisno"organization"usingMACaddresses,this

addressingtechniqueisknownasaflataddressspace.IP

addresses,however,aredividedintotwoparts:anetwork

addressandahostaddress.Thus,IPaddresses(whichare

describedingreaterdetailinChapter24)allowforroutingand

otherfunctions.MACaddresses,however,aregenerallyused

onlyonthelocalLAN,whichconsistsofamuchsmallernumber

ofnetworknodes.

OnaLAN,whichisusedwhenonlyahandfulofnetwork

devicesareconnected(uptoafewhundredorevenafew

thousand),aMACaddressissufficientforgettingthedata

deliveredtotheappropriatenode.Thedataframeisbroadcast

toallnodesunlessaswitchisused.TheswitchlearnstheMAC

addressesforattacheddevicesandeliminatesthe"broadcast."

WhenanoderecognizesthataframecontainsitsMACaddress,

itrespondsbygrabbingtheframe,andfromthatpointonward

theMACaddressisusedtocommunicatebetweenthetwo



nodes.Manynetworkdeviceshavethecapabilityofmaintaining

atableofMACaddressestoIPaddresses.Thisinformation

staysinthetableforashortperiodincaseadditional

communicationstakeplace.Eventuallytheentryisagedoutof

thetableasnewaddresspairsareadded.



Tip

DistinguishingbetweenMACandIPaddressesis

simple.MACaddressesareusedforanydeviceona

LAN,whetheritbeacomputer,printer,orrouterfor

exchangingdata.IPaddressesareusedtoexchange

databetweenLANs.AftertheIPprotocolhas

deliveredthedatatoarouterconnectedtoaLAN,

theMACaddressisusedtoexchangedatabetween

therouterandthedestinationdevice.Andall

communicationsonaLANusetheMACaddressfor

communications.



ThePhysicalLayer

AtthebottomoftheOSImodel,youwillfindthephysical

componentsthatperformthefunctionsneededtotransmitthe

datapasseddownfromhigherlayers.Theseincludethe

networkadaptercardandthenetworkmediacopperwireor

fiber-opticcables,forexample.

Itiseasytounderstandthepacketorframethatahigher-level

protocolconstructs,whichyouwilllearnaboutinfollowing

chapters.Theactualsignalingmechanismatthephysicallayer,

however,canbedifferentdependingonthenetworkmedia,and

thismechanismcanbedifferentdependingonthetransmission



protocolusedforthenetworkmedia.Forexample,10BASE-T

and100BASE-TandGigabitEthernettransmissionsacrossa

coppernetworkmediausedifferentmethodstosendbitsof

dataacrossthenetwork.Similarly,themechanismsusedto

senddataacrossafiber-opticcablewilldependontheprotocol

used.

Considertheprocessofsendingsinglebitsofinformationacross

anetworkcable.Youmightexpectthateachbitisrepresented

bysomekindofstatechange(electricalorphoto-optic)onthe

cable.Thisisnotalwaysthecase.Instead,atthephysicallevel,

varioustechniquesareused.Itmaybeassimpleasvaryingthe

voltageonacopperwireorasinvolvedasusingstatistical

methodstovarythevoltageandfrequencyofthesignal.A

goodexampleofthephysicalmethodfortransmittingbytesof

informationacrossanetworkisFibreChannel,inwhich10bits

areusedtosend8bitsofdata.Inthiscase,foreachbyteof

informationtherecanbeeitheroneortwopossiblebit

combinationsusedtotransmitthesamebyte!Thisisbecause

FibreChannel,usuallyimplementedusingfiber-opticcables,

triestomaintaina"runningdisparity"onthenetworkmedia.

Thisisforseveralreasons,whicharecoveredindetailin

Chapter11,"NetworkAttachedStorageandStorageArea

Networks."Anotherexampleofthis,ManchesterEncoding,is

describedinChapter13,"Ethernet:TheUniversalStandard."



OtherPhysicalLayerComponents

Thephysicallayerstandardsestablishedbythe802.*

committeeinvolvemanyotherconcepts,suchasbridgesand

theprotocolsassociatedwiththesedevices,liketheSpanning

TreeAlgorithm.AfteryougetpasttheLAN/MANspecifications,

theroutingterrainisthenextstep.Becauseroutingimplies

connectingvariousphysicalLANs,routingisbeyondthescope

oftheLAN/MANcommittee.



ThemostwidelyusedLANtechnologyinusetodayisEthernet.

Andthisprotocolanditsassociatedtechnologieshavebeen

extendedovertimetoallowforend-to-endEthernet

connectionsacrossMANs.Thevarious802.*standardsfor

Ethernet,Token-Ring,andothernetworkingtechnologiesare

exploredinthefollowingsections.



IEEE802.1:BridgingandManagement

The802.1standardsconcernbridging.Bridginginvolves

connectingtwoormorenetworksusinganintermediary

networkdevicethatservesoneortwopurposes.First,abridge

canbeusedtoconnectseveralLANsegmentssothattraffic

betweennodesonthenetworkisconfinedtothatLANsegment.

Second,abridgecanbeusedtotranslatebetweendifferent

protocols.

Sincetheoriginalpublicationofthisstandard,therehavebeen

severalotherstandardsthatrelatetotheoriginal802.1.For

example,IEEE802.1Qdiscussesusingbridgestocreatea

virtualLAN.IEEE802.1xprovidesfortheuseofaMACbridge

tocreateavirtualLAN.Bothofthesearediscussedinfurther

detailinChapter9,"VirtualLANs."



IEEE802.2:LogicalLinkControl

Asdescribedearlier,theIEEEspecificationsdividetheDataLink

layerintotwoparts:theLogicalLinkControl(LLC)sublayerand

theMediaAccessControlsublayer.TheLLCsublayerprovides

servicestotheNetworklayerintheOSImodel,independentof

theunderlyingMACsublayer.

Thissublayerprovidesforthreekindsofservice.Type1defines

anunacknowledgedconnectionlessmodelink.Type2definesa



connection-modelink.Type3definesanacknowledged

connectionlessmode.Itisn'timportanttounderstandexactly

whatthesetypesoflinksreallymeanatthispoint.InChapter

25,youwilllearnhowTCPprovidesaconnection-orientedlink,

whereasotherprotocols,suchasUDP,provideaconnectionless

link.TheimportantthingtorememberhereisthattheIEEE802

documentationdefinesthefeaturesandboundariesofthese

typesofconnections.

Type1servicesdonotneedany"setup"beforecommunications

canbegin.Thistypeofserviceprovidesnomechanismsforflow

controlorerrordetection.

Type2servicesdictatethatalogicallinkmustbeestablished

beforedatacommunicationscanbegin.Anexampleofthisis

theTCPprotocol,whichusesa"handshake"exchangeof

networkpacketstosetupthelinkbeforetheactualdata

exchangecanbegin.Thistypeofservicedoesprovideforerror

detectionandflowcontrol.

Type3servicesprovideforaconnectionlesslink,inwhichno

setupisrequired.However,acknowledgmentsareusedto

ensurethatnetworkpacketsarereceivedintactandinthe

orderinwhichtheyaresent.



IEEE802.3:CSMA/CDAccessMethod

Untilthedevelopmentoffull-duplexswitches,themethodused

bynodesonanEthernetnetworktogainaccesstotheshared

networkmediawascalledCarrierSenseMultiple

Access/CollisionDetect,orCSMA/CD.Thissimplymeansthat

beforeattemptingtosenddataonasharedLANsegment,the

computer(orothernetworkeddevice)wouldfirstlisten(carrier

sense)todeterminewhetheranotherdeviceisalready

transmittingdata(multipleaccess).Ifnot,thenodecouldbegin

totransmitdataontothenetwork.Ifmorethanonenode



sensesthatthenetworkmediaisnotbeingusedandboth

nodesbegintotransmitdataataboutthesametime,a

"collision"occurs(collisiondetect).Inthatcase,eachnodewill

stoptransmittingforasemi-randomintervalbeforeattempting

totransmitagain.

ForsmallLANsthistechniqueprovidesaninexpensivemethod

toallowcomputerstouseasharednetworkmedia.Asnetworks

havegrowninsize,switcheshavereplacedhubsinmost

networks.Switchesremovethe"collisiondomain"sothat

communicationstakeplacebetweenjusttheswitchportand

thecomputerconnectedtothatport.Iftheswitchoperatesin

half-duplexmode,acollisioncanoccuriftheswitchandthe

attachedcomputerbothtrytotransmitdataatthesametime.

Infull-duplexmode,whichisthemostwidelyusedmodetoday,

theswitchportandtheattachedcomputerdonotsharethe

samewires,butinsteadeachhasadedicatedsetofwiresso

thattheswitchcansenddatawhiletheattachedcomputeris

sendingdatatotheswitch.

ItisimportanttounderstandtheCSMA/CDtechnique,however,

sothatyoucanseehowEthernethasevolvedfromashared

medianetworkingtechnologytotheswitchedenvironmentused

today.FormoreinformationaboutCSMA/CD,seeChapter13.



IEEE802.4:Token-PassingBusAccessMethod

andIEEE802.5:Token-RingAccessMethod

Token-RingandToken-Bustechnologieshavealotincommon.

Theybothassumearingtopology,andatokenframeispassed

fromonenodetoanother.Whenanodeonthenetworkneeds

totransmitdata,itwaitsuntilitreceivesthetokenframeand

thentransmitsadataframe.Thedataframetravelsaroundthe

ringuntilthedestinationnodereceivesit.Uponsuccessfully

receivingadataframe,thedestinationnodesetsafewbitsin



theframetoindicatethatitwassuccessfullyreceivedand

retransmitsthemodifiedframeonthenetwork.Whenthe

sendingnodereceivestheframeitoriginallysent,itcancheck

thebitstoseethatthedatawasreceived,anditthentransmits

atokenframesothatanothernodecanusethenetwork.

ThemajordifferencebetweentheToken-BusandtheTokenRingnetworkisthattheToken-Ringnetworkisphysicallywired

inaringtopology.Thatis,thetransmitterofanodeis

connectedtothereceiverofthenextnodeinthering,untilthe

lastnodeintheringconnectsbacktothereceiverofthefirst

nodeinthering.WhenaToken-Busisused,asinglenetwork

mediaisusedthatconnectsallnodes,similartoabustopology

inearlyEthernetnetworks.However,theringtopologyis

maintainedasalogicalring.InsteadofusingtheCSMA/CD

methodtoaccessthesharedbusmedia,eachnodeona

networkpassesthetokenframefromonenodetoanother,ina

predeterminedorder,andthusaringformationisstillused.

Token-Ringnetworksarestillinusetoday,thoughtheir

numbersarefaroutweighedbytheinstalledbaseofEthernet

networks.Token-Busnetworksweregenerallyusedinindustrial

situations,suchasfactoryfloors,whereaguaranteedminimum

accesstimewascrucial.DevelopmentofToken-Bustopologies

hasnowbeendiscontinued.ToquotetheIEEE,"These

standardswereadministrativelywithdrawnbytheIEEE

StandardsBoard."AlthoughToken-Ringnetworksarestill

marketedtoday,thespeedsatwhichEthernetnowoperateshas

allbutrenderedToken-Ringtohistory.



IEEE802.7:RecommendedPracticesfor

BroadbandLocalAreaNetworks

Thisstandard,firstpublishedin1989,describedvariousitems

thatwerepertinenttoofferingbroadbandcommunicationsat



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