Tanenbaum《计算机网络》原版课件第3章

TheDataLinkLayerChapter3DataLinkLayerDesignIssues•ServicesProvidedtotheNetworkLayer•Framing•ErrorControl•FlowControlFunctionsoftheDataLinkLayer•Provideserviceinterfacetothenetworklayer•Dealingwithtransmissionerrors•Regulatingdataflow•SlowreceiversnotswampedbyfastsendersFunctionsoftheDataLinkLayer(2)Relationshipbetweenpacketsandframes.ServicesProvidedtoNetworkLayer(a)Virtualcommunication.(b)Actualcommunication.ServicesProvidedtoNetworkLayer(2)Placementofthedatalinkprotocol.FramingAcharacterstream.(a)Withouterrors.(b)Withoneerror.Framing(2)(a)Aframedelimitedbyflagbytes.(b)Fourexamplesofbytesequencesbeforeandafterstuffing.Framing(3)Bitstuffing(a)Theoriginaldata.(b)Thedataastheyappearontheline.(c)Thedataastheyarestoredinreceiver’smemoryafterdestuffing.ErrorDetectionandCorrection•Error-CorrectingCodes•Error-DetectingCodesError-CorrectingCodesUseofaHammingcodetocorrectbursterrors.Error-DetectingCodesCalculationofthepolynomialcodechecksum.ElementaryDataLinkProtocols•AnUnrestrictedSimplexProtocol•ASimplexStop-and-WaitProtocol•ASimplexProtocolforaNoisyChannelProtocolDefinitionsContinuedSomedefinitionsneededintheprotocolstofollow.Thesearelocatedinthefileprotocol.h.ProtocolDefinitions(ctd.)Somedefinitionsneededintheprotocolstofollow.Thesearelocatedinthefileprotocol.h.UnrestrictedSimplexProtocolSimplexStop-and-WaitProtocolASimplexProtocolforaNoisyChannelApositiveacknowledgementwithretransmissionprotocol.ContinuedASimplexProtocolforaNoisyChannel(ctd.)Apositiveacknowledgementwithretransmissionprotocol.SlidingWindowProtocols•AOne-BitSlidingWindowProtocol•AProtocolUsingGoBackN•AProtocolUsingSelectiveRepeatSlidingWindowProtocols(2)Aslidingwindowofsize1,witha3-bitsequencenumber.(a)Initially.(b)Afterthefirstframehasbeensent.(c)Afterthefirstframehasbeenreceived.(d)Afterthefirstacknowledgementhasbeenreceived.AOne-BitSlidingWindowProtocolContinuedAOne-BitSlidingWindowProtocol(ctd.)AOne-BitSlidingWindowProtocol(2)Twoscenariosforprotocol4.(a)Normalcase.(b)Abnormalcase.Thenotationis(seq,ack,packetnumber).Anasteriskindicateswhereanetworklayeracceptsapacket.AProtocolUsingGoBackNPipelininganderrorrecovery.Effectonanerrorwhen(a)Receiver’swindowsizeis1.(b)Receiver’swindowsizeislarge.SlidingWindowProtocolUsingGoBackNContinuedSlidingWindowProtocolUsingGoBackNContinuedSlidingWindowProtocolUsingGoBackNContinuedSlidingWindowProtocolUsingGoBackNSlidingWindowProtocolUsingGoBackN(2)Simulationofmultipletimersinsoftware.ASlidingWindowProtocolUsingSelectiveRepeatContinuedContinuedASlidingWindowProtocolUsingSelectiveRepeat(2)ASlidingWindowProtocolUsingSelectiveRepeat(3)ContinuedASlidingWindowProtocolUsingSelectiveRepeat(4)ASlidingWindowProtocolUsingSelectiveRepeat(5)(a)Initialsituationwithawindowsizeseven.(b)Aftersevenframessentandreceived,butnotacknowledged.(c)Initialsituationwithawindowsizeoffour.(d)Afterfourframessentandreceived,butnotacknowledged.ProtocolVerification•FiniteStateMachinedModels•PetriNetModelsFiniteStateMachinedModels(a)Statediagramforprotocol3.(b)Transmissions.PetriNetModelsAPetrinetwithtwoplacesandtwotransitions.PetriNetModels(2)APetrinetmodelforprotocol3.ExampleDataLinkProtocols•HDLC–High-LevelDataLinkControl•TheDataLinkLayerintheInternetHigh-LevelDataLinkControlFrameformatforbit-orientedprotocols.High-LevelDataLinkControl(2)Controlfieldof(a)Aninformationframe.(b)Asupervisoryframe.(c)Anunnumberedframe.TheDataLinkLayerintheInternetAhomepersonalcomputeractingasaninternethost.PPP–PointtoPointProtocolThePPPfullframeformatforunnumberedmodeoperation.PPP–PointtoPointProtocol(2)Asimplifiedphasediagramforbringalineupanddown.PPP–PointtoPointProtocol(3)TheLCPframetypes.