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1、Chapter4.DataLinkLayerBusinessDataCommunicationsandNetworkingFitzgeraldandDennis,7thEditionCopyright©2002JohnWiley&Sons,Inc.1Copyrightã2002JohnWiley&Sons,Inc.Allrightsreserved.ReproductionortranslationofthisworkbeyondthatnamedinSection117oftheUnitedStatesCopyrightActwithoutthee
2、xpresswrittenconsentofthecopyrightownerisunlawful.RequestsforfurtherinformationshouldbeaddressedtothePermissionsDepartment,JohnWiley&Sons,Inc.Adoptersofthetextbookaregrantedpermissiontomakeback-upcopiesfortheirownuseonly,tomakecopiesfordistributiontostudentsofthecoursethetextbo
3、okisusedin,andtomodifythismaterialtobestsuittheirinstructionalneeds.Undernocircumstancescancopiesbemadeforresale.ThePublisherassumesnoresponsibilityforerrors,omissions,ordamages,causedbytheuseoftheseprogramsorfromtheuseoftheinformationcontainedherein.2Chapter4.LearningObjective
4、sUnderstandtheroleofthedatalinklayerBecomefamiliarwithtwobasicapproachestocontrollingaccesstothemediaBecomefamiliarwithcommonsourcesoferrorandtheirpreventionUnderstandthreecommonerrordetectionandcorrectionmethodsBecomefamiliarwithseveralcommonlyuseddatalinkprotocols3Chapter4.Ou
5、tlineIntroductionMediaAccessControlControlledAccess,Contention,RelativePerformanceErrorControlSourcesofErrors,ErrorPrevention,ErrorDetection,ErrorCorrectionviaRetransmission,ForwardErrorCorrectionDataLinkProtocolsAsynchronousTransmission,AsynchronousFileTransferProtocols,Synchr
6、onousTransmissionTransmissionEfficiencySummary4Introduction5IntroductionThedatalinklayersitsbetweenthephysicalandnetworklayers,organizingphysicallayerbitstreamsintocoherentmessagesthatarepasseduptothenetworklayer.Datalinkprotocolshavethreefunctions:MediaAccessControl:Controllin
7、gwhencomputerstransmit.ErrorControl:Detectingandcorrectingtransmissionerrors.MessageDelineation:Identifyingthebeginningandendofamessage.6MediaAccessControl7MediaAccessControlMediaAccessControlmeanscontrollingwhencomputerstransmit.Itisimportantinsituationswheremorethanonecompute
8、rwantstosenddataatthesametimeoverthesamecircuit,suchas
