Chapter5:TheDataLinkLayerOurgoals:understandprinciplesbehinddatalinklayerservices:errordetection,correctionsharingabroadcastchannel:esslinklayeraddressingreliabledatatransfer,flowcontrol:done!instantiationandimplementationofvariouslinklayertechnologies15:-:ATMandMPLS25:DataLinkLayerLinkLayer:IntroductionSometerminology:municationpatharelinkswiredlinkswirelesslinksLANslayer-2packetisaframe,encapsulatesdatagram“link”data-linklayerhasresponsibilityoftransferringdatagramfromonenodetoadjacentnodeoveralink35:DataLinkLayerLinklayer:contextDatagramtransferredbydifferentlinkprotocolsoverdifferentlinks:.,onfirstlink,framerelayonintermediatelinks,.,mayormaynotproviderdtoverlinktransportationanalogytripfromPrincetontoLausannelimo:PrincetontoJFKplane:JFKtoGenevatrain:ourist=ess=linklayerprotocoltravelagent=routingalgorithmTrafficlights,Airportcontrol,Platformscheduling,45:DataLinkLayerLinkLayerServicesFraming,ess:encapsulatedatagramintoframe,addingheader,essifsharedmedium“MAC”addressesusedinframeheaderstoidentifysource,destdifferentfromIPaddress!Reliabledeliverybetweenadjacentnodeswelearnedhowtodothisalready(chapter3)!seldomusedonlowbiterrorlink(fiber,sometwistedpair)wirelesslinks:higherrorratesQ:whybothlink-levelandend-endreliability?55:DataLinkLayerLinkLayerServices(more)FlowControl:pacingbetweenadjacentsendingandreceivingnodesErrorDetection:errorscausedbysignalattenuation,:signalssenderforretransmissionordropsframeErrorCorrection:receiveridentifiesandcorrectsbiterror(s)withoutresortingtoretransmissionHalf-duplexandfull-duplexwithhalfduplex,nodesatbothendsoflinkcantransmit,butnotatsametime65:municatinglinklayerimplementedin“adaptor”(akaNIC)card,PCMCIcard,:encapsulatesdatagraminaframeaddserrorchecking
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