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《全套英文版《计算机网络》电子课件教案-chapter 5 the data link layer.ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、Chapter5:TheDataLinkLayerOurgoals:understandprinciplesbehinddatalinklayerservices:errordetection,correctionsharingabroadcastchannel:multipleaccesslinklayeraddressingreliabledatatransfer,flowcontrol:done!instantiationandimplementationofvariouslinklaye
2、rtechnologiesOverview:linklayerserviceserrordetection,correctionmultipleaccessprotocolsandLANslinklayeraddressing,ARPspecificlinklayertechnologies:Ethernethibs,bridges,switchesIEEE802.11LANsPPPATM15:DataLinkLayerLinkLayer:settingthecontext25:DataLink
3、LayerLinkLayer:settingthecontexttwophysicallyconnecteddevices:host-router,router-router,host-hostunitofdata:frameapplicationtransportnetworklinkphysicalnetworklinkphysicalMMMMHtHtHnHtHnHlMHtHnHlframephys.linkdatalinkprotocoladaptercard35:DataLinkLaye
4、rLinkLayerServicesFraming,linkaccess:encapsulatedatagramintoframe,addingheader,trailerimplementchannelaccessifsharedmedium,‘physicaladdresses’usedinframeheaderstoidentifysource,destdifferentfromIPaddress!Reliabledeliverybetweentwophysicallyconnectedd
5、evices:welearnedhowtodothisalready(chapter3)!seldomusedonlowbiterrorlink(fiber,sometwistedpair)wirelesslinks:higherrorratesQ:whybothlink-levelandend-endreliability?45:DataLinkLayerLinkLayerServices(more)FlowControl:pacingbetweensenderandreceiversErro
6、rDetection:errorscausedbysignalattenuation,noise.receiverdetectspresenceoferrors:signalssenderforretransmissionordropsframeErrorCorrection:receiveridentifiesandcorrectsbiterror(s)withoutresortingtoretransmission55:DataLinkLayerLinkLayer:Implementatio
7、nimplementedin“adapter”e.g.,PCMCIAcard,Ethernetcardtypicallyincludes:RAM,DSPchips,hostbusinterface,andlinkinterfaceapplicationtransportnetworklinkphysicalnetworklinkphysicalMMMMHtHtHnHtHnHlMHtHnHlframephys.linkdatalinkprotocoladaptercard65:DataLinkLa
8、yerErrorDetectionEDC=ErrorDetectionandCorrectionbits(redundancy)D=Dataprotectedbyerrorchecking,mayincludeheaderfieldsErrordetectionnot100%reliable!protocolmaymisssomeerrors,butrarelylargerEDCfieldyieldsbetterdetectionandcorrection75:DataLinkLayerPari
