IP網(wǎng)絡(luò)技術(shù)基礎(chǔ)課件(英文)

1End-to-EndProtocolOutline

SimpleDemultiplexer(UDP)ReliableByte-Stream(TCP)ConnectionEstablishment/TerminationSlidingWindowRevisitedFlowControl1End-to-EndProtocolOutline2TheLayeredNetworkStackPhysicalLayerApplicationLayerTransportLayer(TCP/UDP)NetworkLayer(IP)DataLinkLayerInternetStackPhysicalLayerSessionLayerTransportLayerNetworkLayerDataLinkLayerOSIStackPresentationLayerApplicationLayer2TheLayeredNetworkStackPhys3End-to-EndProtocolsUnderlyingbest-effortnetworkdropmessagesre-ordersmessagesdeliversduplicatecopiesofagivenmessagelimitsmessagestosomefinitesizedeliversmessagesafteranarbitrarilylongdelayCommonend-to-endservicesguaranteemessagedeliverydelivermessagesinthesameordertheyaresentdeliveratmostonecopyofeachmessagesupportarbitrarilylargemessagessupportsynchronizationallowthereceivertoflowcontrolthesendersupportmultipleapplicationprocessesoneachhost3End-to-EndProtocolsUnderlyin4Transportlayerusesthenetworklayer,tosendandreceivedata.TransportProtocolDataUnit(TPDU)EachlayeraddsitspartTCPsegment,IPpacket,DatalinkframeOverviewofTransportLayer

4Transportlayerusesthenetw5OverviewofTransportLayer

(cont.)5OverviewofTransportLayer

(6Twotypesoftransportservicesconnection-orientedconnectionlessEnd-to-EndProtocols6Twotypesoftransportservic7SimpleDemultiplexor(UDP)TransportprotocolaboveIPsimplypassesIPthroughtotheupper(application)layersUnreliableandunordereddatagramserviceAddsmultiplexingNoflowcontrolEndpointsidentifiedbyportsservershavewell-knownportsFTP-21,Telnet-23,http-80,pop-110,DNS-537SimpleDemultiplexor(UDP)Tra8UDP“Features”Givesapp’stheoptiontosendpacketsunreliablyUsefulformulticastapp’sLowdelaytransmissionforinteractivetext/audio/videoMinimalconnectionstate:“connectionless”MinimalconnectionsetuptimeNocongestioncontrol–blastawayBuildownapplication-levelprotocolontopofUDP8UDP“Features”Givesapp’sthe9UDPUDPHeader:Only8bytes!(vs.IP20bytesheader)SourceportforUDPsendingprocessDestportforUDPreceivingprocessLengthinbytesofUDPheader+payloadChecksumoverUDPheader+payloadSourcePort#Dest.Port#UDPlengthChecksum1632UDPpayloaddataUDPpayloadIPhdrUDPhdrErrorDetection9UDPUDPHeader:SourcePort#De10ErrorDetectionWhyisthereerrordetectioninthetransportlayergiventhatthesamefunctionisprovidedbythedatalinklayerReliabletransmissionalongeachlinkisstillnoguaranteeoferror-freetransmissionbetweenthesourceandthedestination.10ErrorDetectionWhyisthere11ErrorDetection(cont.)11ErrorDetection(cont.)12TCPOverviewConnection-orientedTCPprovides:Reliabledeliveryofpackets,Streamorin-orderdeliveryApplicationprocessWritebytesTCPSendbufferSegmentSegmentSegmentTransmitsegmentsApplicationprocessReadbytesTCPReceivebuffer………Fullduplex Flowcontrol:keepsenderfromoverrunningreceiverCongestioncontrol:keepsenderfromoverrunningnetwork12TCPOverviewConnection-orien13TransportControlProtocolProvidesareliableend-to-endbytestreamoveranunreliablenetworksuchasIP.Providesconnectionorienteduser-to-userserviceconnectionmanagementNointermediatenodesareinvolvedinconnectionestablishment.TCPserviceisobtainedbyhavingboththesenderandreceivercreateendpointscalledsockets.Eachsocketisassociated(bound)withIPaddressofthehost16-bitnumberlocaltothehostcalledaport13TransportControlProtocolPr14TransportControlProtocol

(cont.)14TransportControlProtocol

(15DataLinkVersusTransportPotentiallyconnectsmanydifferenthostsneedexplicitconnectionestablishmentandterminationPotentiallydifferentRTTneedadaptivetimeoutmechanismPotentiallylongdelayinnetworkneedtobepreparedforarrivalofveryoldpacketsPotentiallydifferentcapacityatdestinationneedtoaccommodatedifferentnodecapacityPotentiallydifferentnetworkcapacityneedtobepreparedfornetworkcongestion15DataLinkVersusTransportPo16TCPSegmentAsegmentconsistsofafixed20-byteheader(plusanoptionalpart)followedbyzeroormoredatabytes16TCPSegmentAsegmentconsist17TCPSegment(cont.)Sourceport(16bits)–Specifiestheapplicationsendingthesegment.17TCPSegment(cont.)Sourcepo18TCPSegment(cont.)Destinationport(16bits)–Identifiestheapplicationtowhichthesegmentissent.18TCPSegment(cont.)Destinati19TCPSegment(cont.)Sequencenumber(32bits)–Containsthesequencenumberofthefirstbyteofdata.19TCPSegment(cont.)Sequence20TCPSegment(cont.)Acknowledgmentnumber(32bits)–ContainsthebytesequencenumberwhichthereceivingTCPentityexpectstoreceivenext.20TCPSegment(cont.)Acknowled21TCPSegment(cont.)Headerlength(4bits):thesizeoftheTCPheader.21TCPSegment(cont.)Headerle22TCPSegment(cont.)Flags(6bits)–Controlfunctionsforestablishingandremovingconnectionsetc.IncludeURG,ACK,PSH,RST,SYN,FIN.22TCPSegment(cont.)Flags(623TCPSegment(cont.)Window(16bits)–TellsthereceivingTCPentityhowmanydatabytesthesendingTCPentitycanaccept.23TCPSegment(cont.)Window(124TCPSegment(cont.)Checksum(16bits)–Usedfortransportlayererrordetection.–

pseudoheader(12Bytes)+TCPheader+data24TCPSegment(cont.)Checksum25TCPSegment(cont.)Urgentpointer(16bits)–Signalthereceivertodeliverthedatatothehigherlayerasquicklyaspossible.25TCPSegment(cont.)Urgentpo26TCPSegment(cont.)Options/padding-maximumsegmentsize26TCPSegment(cont.)Options/p27SegmentFormat(cont)Eachconnectionidentifiedwith4-tuple:(SrcPort,SrcIPAddr,DsrPort,DstIPAddr)Slidingwindow+flowcontrolacknowledgment,SequenceNum,AdvertisedWinowSenderData(SequenceNum)Acknowledgment+AdvertisedWindowReceiver27SegmentFormat(cont)Eachco28ConnectionEstablishmentActiveparticipant(client)Passiveparticipant(server)SYN,SequenceNum=xSYN+ACK,SequenceNum=

y,ACK,Acknowledgment=y

+1Acknowledgment=x

+1SequenceNum=x+1

28ConnectionEstablishmentActi29ConnectionTermination29ConnectionTermination30StateTransitionDiagramCLOSEDLISTENSYN_RCVDSYN_SENTESTABLISHEDCLOSE_WAITLAST_ACKCLOSINGTIME_WAITFIN_WAIT_2FIN_WAIT_1PassiveopenCloseSend/SYNSYN/SYN+ACKSYN+ACK/ACKSYN/SYN+ACKACKClose/FINFIN/ACKClose/FINFIN/ACKACK+FIN/ACKTimeoutaftertwosegmentlifetimesFIN/ACKACKACKACKClose/FINCloseCLOSEDActiveopen/SYN30StateTransitionDiagramCLOS31SlidingWindowRevisitedSendingsideLastByteAcked<=LastByteSentLastByteSent<=LastByteWrittenbufferbytesbetweenLastByteAckedandLastByteWrittenSendingapplicationLastByteWrittenTCPLastByteSentLastByteAckedReceivingapplicationLastByteReadTCPLastByteRcvdNextByteExpectedReceivingsideLastByteRead<NextByteExpectedNextByteExpected<=LastByteRcvd+1bufferbytesbetweenNextByteReadandLastByteRcvd31SlidingWindowRevisitedSend32FlowControlSendbuffersize:MaxSendBufferReceivebuffersize:MaxRcvBufferReceivingsideLastByteRcvd-LastByteRead<=MaxRcvBufferAdvertisedWindow=MaxRcvBuffer–((NextByteExpected-1)-NextByteRead)SendingsideLastByteSent-LastByteAcked<=AdvertisedWindowEffectiveWindow=AdvertisedWindow-(LastByteSent-LastByteAcked)LastByteWritten-LastByteAcked<=MaxSendBufferblocksenderif(LastByteWritten-LastByteAcked)+y>MaxSenderBufferAlwayssendACKinresponsetoarrivingdatasegmentPersistwhenAdvertisedWindow

=032FlowControlSendbuffersize33FlowControlTransportprotocolsresemblethedatalinkprotocolsFlowcontrol,errorcontrol,sequencingAslidingwindowisusedforflowcontrolDifferencesArouterusuallyhasonlyafewlinkstoothers,whileatransportentitymayhavenumerousconnections.Thisdifferencemakesitimpracticaltoimplementadatalinkbufferingstrategyinthetransportlayer.Thereceivermaynotdedicatespecificbufferstospecificconnections.33FlowControlTransportprotoc34FlowControlDynamicbuffermanagement-creditmechanismInitially,thesenderrequestsacertainnumberofbuffers(credit),basedonitsperceivedneeds.Thereceivergrantsasmanyoftheseasitcanafford.EverytimethesendertransmitsaTPDU,itdecreasesitsallocation(credit),stoppingwhentheallocation(credit)reacheszero.Thereceiverreturnsbothacknowledgmentsandbufferallocations(credit).34FlowControlDynamicbufferm35MoveforwardbyACK1002003004005006007008009001012013014015016017018011SenderwindowDatathatcanbesent不可發(fā)送pointerSenderwantstosend900bytes–9segments(100byteseachsegment).

Thesenderwindowis500bytes.SendercanmovethewindowforwardbytheACKfromthereceiver.Inaddition,thesendermaintainapointertoidentifythedatawhichhavebeensent.Datathatcannotbesent35MoveforwardbyACK100200300361002003004005006007008009001012013014015016017018011可發(fā)送不可發(fā)送pointer1002003004005006007008009001012013014015016017018011發(fā)送窗口可發(fā)送不可發(fā)送SendwindowmovesforwardThesenderhavesend400bytes.AndthesenderonlyreceivetheACKofthetop200bytes.Thewindowis500.Sothesendercanstillsend300bytes.

Sent&acked已發(fā)送但未被確認SenderwindowDatathatcanbesentMoveforwardbyACK500600700800900501601701801不可發(fā)送DatathatcannotbesentpointerSent&NotackedDatathatcanbesentDatathatcannotbesent361002003004005006007008009001371002003004005006007008009001012013014015016017018011Sent&acked可發(fā)送pointerSendwindowreduceThesenderreceivetheACKofthefollowing200bytes.Thewindowischangedto400.Sothesendercansend400bytes.1002003004005006007008009001012013014015016017018011可發(fā)送不可發(fā)送pointerSendwindowmovesforwardSent&acked已發(fā)送但未被確認Sent&Notack