计算机网络英文版复习知识教材课程PPT格式课件下载.ppt

计算机网络英文版复习知识教材课程PPT格式课件下载.ppt

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ComputerNetworkingFinalReview,JinghuiQin,Content,ComputerNetworksandtheInternetApplicationLayerTransportLayerTheNetworkLayerTheLinkandLocalAreaNetworksWirelessandMobileNetworks,ComputerNetworksandtheInternet,Somebasicconceptsprotocolcircuitswitchingpacketswitchingetc.Delay,LossandThroughputinPacket-SwitchedNetworksprocessingdelayqueuingdelaytransmissiondelay,ComputerNetworksandtheInternet,propagationdelayend-to-enddelaycomputationthroughput:

@#@instantaneous,averageProtocolLayersandTheirServiceModelsSeven-layerISOOSIreferencemodelFive-layerInternetprotocolstackThefunctionofeachlayer,ComputerNetworksandtheInternet,Problem1-P5,ComputerNetworksandtheInternet,Problem1-P5,ComputerNetworksandtheInternet,Solution1-P5,ComputerNetworksandtheInternet,Problem2-P17,ComputerNetworksandtheInternet,Solution2-P17Throughput=minRs,Rc,R/M,ApplicationLayer,SomebasicconceptsclientserversocketTransportServicesProvidedbyInternetTCPservices:

@#@connection-oriented&@#@reliabledatatransferUDPservicesApplication-LayerProtocol,ApplicationLayer,HTTPNon-persistentandPersistentHTTPMessageFormatRequestMessageResponseMessageCookies,ApplicationLayer,FTPtwoparallelconnectionsout-of-band&@#@in-bande-mailSMTPPOP3IMAP,ApplicationLayer,DNSServiceprovidedbyDNSDNSWorkingMechanismDNSRecordsandMessage,ApplicationLayer,Problem-P2,ApplicationLayer,Problem-P2,ApplicationLayer,Problem-P2,ApplicationLayer,Solution-P2a）Thedocumentrequestwashttp:

@#@/gaia.cs.umass.edu/cs453/index.html.TheHost:

@#@fieldindicatestheserversnameand/cs453/index.htmlindicatesthefilename.b）ThebrowserisrunningHTTPversion1.1,asindicatedjustbeforehtefirstpair.c）Thebrowserisrequestingapersistentconnection,asindicatedbytheConnection:

@#@keep-alive.,ApplicationLayer,Solution-P2d）Thisisatrickquestion.ThisinformationisnotcontainedinanHTTPmessageanywhere.SothereisnowaytotellthisfromlookingattheexchangeofHTTPmessagesalone.OnewouldneedinformationfromtheIPdatagrams（thatcarriedtheTCPsegmentthatcarriedtheHTTPGETrequest）toanswerthisquestion.,TransportLayer,UDPUDPSegmentStructureUDPChecksumTheadvantagesofUDPPrinciplesofReliableDataTransferSRGBN,TransportLayer,TCPTCPSegmentStructureTCPflowcontrolTCPcongestcontrolAIMDSlowstartReactionToTimeoutEvents,TransportLayer,Problem1-P23ConsidertransferringanenormousfileofLbytesfromHostAtoHostB.AssumeanMSSof1,460bytes.a.WhatisthemaximumvalueofLsuchthatTCPsequencenumbersarenotexhausted?

@#@RecallthattheTCPsequencenumberfieldhas4bytes.,TransportLayer,Problem1-P23b.FortheLyouobtainin（a）,findhowlongittakestotransmitthefile.Assumethatatotalof66bytesoftransport,network,anddata-linkheaderareaddedtoeachsegmentbeforetheresultingpacketissentoutovera100Mbpslink.IgnoreflowcontrolandcongestioncontrolsoAcanpumpoutthesegmentsbacktobackandcontinuously.,TransportLayer,Solution1-P23,TransportLayer,Solution1-P23,TransportLayer,Problem2-P34,TransportLayer,Problem2-P34,TransportLayer,Problem2-P34,TransportLayer,Solution2-P34a）TCPslowstartisoperatingintheintervals1,6and23,26b）TCPcongestionadvoidanceisoperatingintheintervals6,16and17,22c）Afterthe16thtransmissionround,packetlossisrecognizedbyatripleduplicateACK.Iftherewasatimeout,thecongestionwindowsizewouldhavedroppedto1.,TransportLayer,Solution2-P34d）Afterthe22ndtransmissionround,segmentlossisdetectedduetotimeout,andhencethecongestionwindowsizeissetto1.e）Thethresholdisinitially32,sinceitisatthiswindowsizethatslowtartstopsandcongestionavoidancebegins.f）Thethresholdissettohalfthevalueofthecongestionwindowwhenpacketlossisdetected.Whenlossisdetectedduringtransmissionround16,thecongestionwindowssizeis42.Hencethethresholdis21duringthe18thtransmissionround.,TransportLayer,Solution2-P34g）Thethresholdissettohalfthevalueofthecongestionwindowwhenpacketlossisdetected.Whenlossisdetectedduringtransmissionround22,thecongestionwindowssizeis26.Hencethethresholdis13duringthe24thtransmissionround.i）Thecongestionwindowandthresholdwillbesettohalfthecurrentvalueofthecongestionwindow（8）whenthelossoccurred.Thusthenewvaluesofthethresholdandwindowwillbe4.,TransportLayer,Solution2-P34H）Duringthe1sttransmissionround,packet1issent;@#@packet2-3aresentinthe2ndtransmissionround;@#@packets4-7aresentinthe3rdtransmissionround;@#@packets8-15aresentinthe4thtransmissionround;@#@packets15-31aresentinthe5thtransmissionround;@#@packets32-63aresentinthe6thtransmissionround;@#@packets6496aresentinthe7thtransmissionround.Thuspacket70issentinthe7thtransmissionround.,TheNetworkLayer,Virtual-CircuitNetworksDatagramNetworkslongestpre