802.3-2005-section5

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1、Informationtechnology—Telecommunicationsandinformationexchangebetweensystems—Localandmetropolitanareanetworks—Specificrequirements—Part3:CarrierSenseMultipleAccesswithCollisionDetection(CSMA/CD)accessmethodandphysicallayerspecificationsSECTIONFIVE:ThissectionincludesClause56

2、throughClause67andAnnex58AthroughAnnex67A.56.IntroductiontoEthernetforsubscriberaccessnetworks56.1OverviewEthernetforsubscriberaccessnetworks,alsoreferredtoas“EthernetintheFirstMile”,orEFM,combinesaminimalsetofextensionstotheIEEE802.3MediaAccessControl(MAC)andMACControlsubla

3、yerswithafamilyofPhysicalLayers.ThesePhysicalLayersincludeopticalfiberandvoicegradecoppercablePhysicalMediumDependentsublayers(PMDs)forpoint-to-point(P2P)connectionsinsubscriberaccessnetworks.EFMalsointroducestheconceptofEthernetPassiveOpticalNetworks(EPONs),inwhichapoint-to

4、-multipoint(P2MP)networktopologyisimplementedwithpassiveopticalsplitters,alongwithextensionstotheMACControlsublayerandReconciliationsublayeraswellasopticalfiberPMDstosupportthistopology.Inaddition,amechanismfornetworkOperations,Administration,andMaintenance(OAM)isincludedtof

5、acilitatenetworkoperationandtroubleshooting.100BASE-LX10extendsthereachof100BASE-Xtoachieve10kmoverconventionalsingle-modetwo-fibercabling.TherelationshipsbetweentheseEFMelementsandtheISO/IECOpenSystemInterconnection(OSI)referencemodelareshowninFigure56–1forpoint-to-pointtop

6、ologies,andFigure56–2forpoint-to-multipointtopologies.AnimportantcharacteristicofEFMisthatonlyfullduplexlinksaresupported.AsimplifiedfullduplexMACisdefinedinAnnex4AforuseinEFMnetworks.P2MPapplicationsmustusethissimplifiedfullduplexMAC.EFMCopperapplicationsmayuseeitherthissim

7、plifiedfullduplexMACortheClause4MACoperatinginhalfduplexmodeasdescribedin61.1.4.1.2.AllotherEFMP2PapplicationsmayuseeitherthissimplifiedfullduplexMACortheClause4MACoperatinginfullduplexmode.56.1.1SummaryofP2PsublayersEFMP2Psupportsoperationatseveraldifferentbitrates,dependin

8、gonthecharacteristicsoftheunderlyingmedium.Inthecaseofpoint-to-pointoptical