本文深入探讨了数据链路层的设计问题，包括网络层服务、帧定界、错误检测与控制、流量控制等核心概念。介绍了帧定界的几种方法，如字节计数、标志字节与位填充，以及错误检测码如汉明码、卷积码等。同时，详细阐述了滑动窗口协议的工作原理，如简单的停止等待协议、Go-Back-N和选择重传协议。此外，还讨论了实际应用中的数据链路协议，如Packet over SONET和ADSL技术，并分析了其协议栈和帧格式。
TheDataLinkLayer,Chapter3,DataLinkLayerDesignIssues,NetworklayerservicesFramingErrorcontrolFlowcontrol,PacketsandFrames,Relationshipbetweenpacketsandframes.,NetworkLayerServices,(a)Virtualcommunication.(b)Actualcommunication.,PossibleServicesOffered,Unacknowledgedconnectionlessservice.Acknowledgedconnectionlessservice.Acknowledgedconnection-orientedservice.,FramingMethods,Bytecount.Flagbyteswithbytestuffing.Flagbitswithbitstuffing.Physicallayercodingviolations.,Framing(1),Abytestream.(a)Withouterrors.(b)Withoneerror.,Framing(2),Aframedelimitedbyflagbytes.Fourexamplesofbytesequencesbeforeandafterbytestuffing.,Framing(3),Bitstuffing.(a)Theoriginaldata.(b)Thedataastheyappearontheline.(c)Thedataastheyarestoredinthereceiver’smemoryafterdestuffing.,ErrorDetectionCodes(1),Hammingcodes.Binaryconvolutionalcodes.Reed-Solomoncodes.Low-DensityParityCheckcodes.,ErrorDetectionCodes(2),Exampleofan(11,7)Hammingcodecorrectingasingle-biterror.,ErrorDetectionCodes(3),TheNASAbinaryconvolutionalcodeusedin802.11.,Error-DetectingCodes(1),Linear,systematicblockcodesParity.Checksums.CyclicRedundancyChecks(CRCs).,Error-DetectingCodes(2),Interleavingofparitybitstodetectabursterror.,Error-DetectingCodes(3),ExamplecalculationoftheCRC,ElementaryDataLinkProtocols(1),UtopianSimplexProtocolSimplexStop-and-WaitProtocolError-FreeChannelSimplexStop-and-WaitProtocolNoisyChannel,ElementaryDataLinkProtocols(2),Implementationofthephysical,datalink,andnetworklayers.,ElementaryDataLinkProtocols(3),Somedefinitionsneededintheprotocolstofollow.Thesedefinitionsarelocatedinthefileprotocol.h.,...,ElementaryDataLinkProtocols(4),Somedefinitionsneededintheprotocolstofollow.Thesedefinitionsarelocatedinthefileprotocol.h.,...,ElementaryDataLinkProtocols(5),Somedefinitionsneededintheprotocolstofollow.Thesedefinitionsarelocatedinthefileprotocol.h.,UtopianSimplexProtocol(1),Autopiansimplexprotocol.,...,UtopianSimplexProtocol(2),Autopiansimplexprotocol.,SimplexStop-and-WaitProtocolforaNoisyChannel(1),Asimplexstop-and-waitprotocol.,...,SimplexStop-and-WaitProtocolforaNoisyChannel(2),Asimplexstop-and-waitprotocol.,SlidingWindowProtocols(1),Apositiveacknowledgementwithretransmissionprotocol.,...,SlidingWindowProtocols(2),Apositiveacknowledgementwithretransmissionprotocol.,...,SlidingWindowProtocols(3),Apositiveacknowledgementwithretransmissionprotocol.,SlidingWindowProtocols(4),Aslidingwindowofsize1,witha3-bitsequencenumber.(a)Initially.(b)Afterthefirstframehasbeensent.,SlidingWindowProtocols(5),Aslidingwindowofsize1,witha3-bitsequencenumber(c)Afterthefirstframehasbeenreceived.(d)Afterthefirstacknowledgementhasbeenreceived.,One-BitSlidingWindowProtocol(1),A1-bitslidingwindowprotocol.,...,One-BitSlidingWindowProtocol(2),A1-bitslidingwindowprotocol.,...,One-BitSlidingWindowProtocol(3),A1-bitslidingwindowprotocol.,One-BitSlidingWindowProtocol(4),Twoscenariosforprotocol4.(a)Normalcase.(b)Abnormalcase.Thenotationis(seq,ack,packetnumber).Anasteriskindicateswhereanetworklayeracceptsapacket,ProtocolUsingGo-Back-N(1),Pipelininganderrorrecovery.Effectofanerrorwhen(a)receiver’swindowsizeis1,ProtocolUsingGo-Back-N(2),Pipelininganderrorrecovery.Effectofanerrorwhen(b)receiver’swindowsizeislarge.,ProtocolUsingGo-Back-N(3),Aslidingwindowprotocolusinggo-back-n.,...,ProtocolUsingGo-Back-N(4),Aslidingwindowprotocolusinggo-back-n.,...,ProtocolUsingGo-Back-N(5),Aslidingwindowprotocolusinggo-back-n.,...,ProtocolUsingGo-Back-N(6),Aslidingwindowprotocolusinggo-back-n.,...,ProtocolUsingGo-Back-N(7),Aslidingwindowprotocolusinggo-back-n.,...,ProtocolUsingGo-Back-N(8),Aslidingwindowprotocolusinggo-back-n.,...,ProtocolUsingGo-Back-N(9),Aslidingwindowprotocolusinggo-back-n.,ProtocolUsingGo-Back-N(10),Simulationofmultipletimersinsoftware.(a)Thequeuedtimeouts(b)Thesituationafterthefirsttimeouthasexpired.,ProtocolUsingSelectiveRepeat(1),Aslidingwindowprotocolusingselectiverepeat.,...,ProtocolUsingSelectiveRepeat(2),Aslidingwindowprotocolusingselectiverepeat.,...,ProtocolUsingSelectiveRepeat(3),Aslidingwindowprotocolusingselectiverepeat.,...,ProtocolUsingSelectiveRepeat(4),Aslidingwindowprotocolusingselectiverepeat.,...,ProtocolUsingSelectiveRepeat(5),Aslidingwindowprotocolusingselectiverepeat.,...,ProtocolUsingSelectiveRepeat(6),Aslidingwindowprotocolusingselectiverepeat.,...,ProtocolUsingSelectiveRepeat(7),Aslidingwindowprotocolusingselectiverepeat.,...,ProtocolUsingSelectiveRepeat(8),Aslidingwindowprotocolusingselectiverepeat.,...,ProtocolUsingSelectiveRepeat(9),Aslidingwindowprotocolusingselectiverepeat.,ProtocolUsingSelectiveRepeat(10),Initialsituationwithawindowofsize7After7framessentandreceivedbutnotacknowledged.Initialsituationwithawindowsizeof4.After4framessentandreceivedbutnotacknowledged.,ExampleDataLinkProtocols,PacketoverSONETADSL(AsymmetricDigitalSubscriberLoop),PacketoverSONET(1),PacketoverSONET.(a)Aprotocolstack.(b)Framerelationships,PacketoverSONET(2),PPPFeaturesSeparatepackets,errordetectionLinkControlProtocolNetworkControlProtocol,PacketoverSONET(3),ThePPPfullframeformatforunnumberedmodeoperation,PacketoverSONET(4),StatediagramforbringingaPPPlinkupanddown,ADSL(AsymmetricDigitalSubscriberLoop)(1),ADSLprotocolstacks.,ADSL(AsymmetricDigitalSubscriberLoop)(1),AAL5framecarryingPPPdata,End,Chapter3,
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