信息通信網(wǎng)絡(luò)概論：第5章 分組交換網(wǎng)-數(shù)據(jù)報網(wǎng)絡(luò)-TCPIP

1TCP/IPandInternet1InternetArchitecture2TheInternetProtocol3TransportLayerProtocols4InternetRouting2TCP/IPandInternet1InternetArchitecture2TheInternetProtocol3TransportLayerProtocols4InternetRouting3WhyInternetworking?Tobuilda“networkofnetworks”orInternetoperatingovermultiple,coexisting,differentnetworktechnologiesprovidingubiquitousconnectivitythroughIPpackettransferachievinghugeeconomiesofscaleGGGGGGHNet5Net5HNet5Net2HNet5Net3HNet5Net1Net5Net44WhyInternetworking?ToprovideuniversalcommunicationservicesindependentofunderlyingnetworktechnologiesprovidingcommoninterfacetouserapplicationsGGGGGGHNet5Net5HNet5Net2HNet5Net3HNet5Net1Net5Net4ReliableStreamServiceUserDatagramService5WhyInternetworking?TosupportdistributedapplicationsAnyapplicationdesignedtooperatebasedonInternetcommunicationservicesimmediatelyoperatesacrosstheentireInternet

RapiddeploymentofnewapplicationsEmail,Web,Peer-to-peer,game,etc.ApplicationsindependentofnetworktechnologyNewnetworkscanbeintroducedbelowOldnetworktechnologiescanberetired6Internethistory最初的ARPANET網(wǎng)絡(luò)196x，美國軍方為互聯(lián)所屬各軍方網(wǎng)絡(luò)，由國防部下屬ARPA(AdvancedResearchProjectAgent)出資贊助大學(xué)開展網(wǎng)絡(luò)互聯(lián)技術(shù)的研究。實驗性網(wǎng)絡(luò)ARPANET。1983年初，美軍將其所有軍事基地的各子網(wǎng)都聯(lián)到了ARPANET上，并全部采用TCP/IP協(xié)議。標(biāo)志著Internet正式誕生。80年代中期的NSFNET20世紀(jì)80年代，美國國家科學(xué)基金會(簡稱NSF)組建了一個從開始就使用TCP/IP協(xié)議的網(wǎng)絡(luò)NSFNET。NSFNET取代ARPANET，于1988年正式成為Internet的主干網(wǎng)。NSFNET采取的是一種層次結(jié)構(gòu)，分為主干網(wǎng)、地區(qū)網(wǎng)與校園網(wǎng)。7Internethistory90年代，商業(yè)機(jī)構(gòu)介入InternetInternet問世后，每年加入Internet的計算機(jī)成指數(shù)式增長。MERIT、MCI與IBM三家商業(yè)公司組建了一個非盈利性的公司ANS，在1990年接管NSFNET構(gòu)成了ANSNET。Internet的商業(yè)化，開拓了其在通信、資料檢索、客戶服務(wù)等方面的巨大潛力，導(dǎo)致了Internet新的飛躍，走向全球。下一代互聯(lián)網(wǎng)Internet21996年美國率先發(fā)起下一代高速互聯(lián)網(wǎng)及其關(guān)鍵技術(shù)的研究。有185所大學(xué)和研究機(jī)構(gòu)加盟了Internet2計劃，建設(shè)了一個獨立的高速網(wǎng)絡(luò)試驗床Abilene，并于1999年1月提供服務(wù)。自1998年以來，其他國家和地區(qū)相繼開展下一代高速互聯(lián)網(wǎng)及其關(guān)鍵技術(shù)的研究。2004年3月，我國第二代CERNET2（中國教育和科研計算機(jī)網(wǎng)）實現(xiàn)了與國際下一代高速互聯(lián)網(wǎng)Internet2的互聯(lián)。InternetArchitectureTheInternetisacollectionofmanynetworksconnectedtogetherbyabunchofbackbones.ThegluethatholdsthewholeInternettogetheristhenetworklayerprotocol,IP(InternetProtocol).

9InternetProtocolApproachIPpacketstransferinformationacrossInternet

HostAIP→router→router…→router→HostBIPInternetlayerineachrouterdeterminesnexthop(router)NetworkinterfacestransferIPpacketsacrossnetworksRouterInternetLayerNetworkInterfaceTransportLayerInternetLayerNetworkInterfaceTransportLayerInternetLayerNetworkInterfaceHostAHostBNet5Net1Net5Net2Net5Net3RouterInternetLayerNetworkInterfaceRouterInternetLayerNetworkInterfaceNet5Net410InternetProtocolstructureARPRARPHardwareInterfaceICMPIGMPIPTCPUDPUserProcessUserProcessUserProcessUserProcessapplicationtransportnetworklinkBest-effortconnectionlesspackettransferReliablestreamserviceUnreliableUserdatagramservice11EncapsulationTCPHeadercontainssource&destinationportnumbersIPHeadercontainssourceanddestinationIPaddresses;transportprotocoltypeEthernetHeadercontainssource&destinationMACaddresses;networkprotocoltypeHTTPRequestTCPheaderHTTPRequestIPheaderTCPheaderHTTPRequestEthernetheaderIPheaderTCPheaderHTTPRequestFCS12TCP/IPandInternet1TheTCP/IPArchitecture2TheInternetProtocol2.1IPAddressing2.2IPpacketstructureandtransmission3TransportLayerProtocols4InternetRouting13TCP/IPandInternet2TheInternetProtocol2.1IPAddressing2.2IPpacketstructureandtransmission14InternetProtocol(IP)Providesbesteffort,connectionlesspacketdeliverymotivatedbyneedtokeeprouterssimpleandbyadaptingtofailureofnetworkelementspacketsmaybelost,outoforder,orevenduplicatedhigherlayerprotocolsmustdealwiththese,ifnecessaryRFCs791,950,919,922,and2474.IPispartofInternetSTDnumber5,whichalsoincludes:InternetControlMessageProtocol(ICMP),RFC792InternetGroupManagementProtocol(IGMP),RFC111215TCP/IPandInternet2TheInternetProtocol2.1IPAddressing2.2IPpacketstructureandtransmission16InternetNames&AddressesInternetNamesEachhosthasauniquenameIndependentofphysicallocationFacilitatememorizationbyhumansDomainNameOrganizationundersingleadministrativeunitHostNameNamegiventohostcomputerUserNameNameassignedtouserInternetAddressesEachhosthasgloballyuniquelogical32bitIPaddressSeparateaddressforeachphysicalconnectiontoanetworkIPaddresshastwoparts:

netidandhostidnetiduniquenetidfacilitatesroutingDottedDecimalNotation: 4 (intj=jthoctet)

DNSresolvesdomainnametoIPaddress17PhysicalAddressesLANs(andothernetworks)assignphysicaladdressestothephysicalattachmenttothenetworkThenetworkusesitsownaddresstotransferpacketsorframestotheappropriatedestinationIPaddressneedstoberesolvedtophysicaladdressateachIPnetworkinterfaceExample:Ethernetuses48-bitaddressesEachEthernetnetworkinterfacecard(NIC)hasgloballyuniqueMediumAccessControl(MAC)orphysicaladdressFirst24bitsidentifyNICmanufacturer;second24bitsareserialnumber00:90:27:96:68:0712hexnumbers18IPAddressingRFC1166EachhostonInternethasunique32bitIPaddressEachaddresshastwoparts:netidandhostidnetidunique&administeredbyInternetCorporationforAssignedNamesandNumbers(ICANN)AmericanRegistryforInternetNumbers(ARIN)ReseauxIPEuropeens(RIPE)AsiaPacificNetworkInformationCentre(APNIC)IPaddressisassignedtonetworkinterfacesratherthanhosts=>separateaddressisrequiredforeachphysicalconnectionofahosttoanetwork;“multi-homed”hosts

Dotted-DecimalNotation:IPaddressof10000000100001110100010000000101isindotted-decimalnotation19ClassesofIPAddresses010netidnetidhostidhostid7bits24bits14bits16bitsClassAClassB126networkswithupto16millionhosts16,382networkswithupto64,000hoststo55to5511netidhostid22bits8bitsClassC02millionnetworkswithupto254hoststo5520MulticastaddressUpto250millionmulticast

groupsatthesametime11multicastaddress28bits10ClassDto55ClassesofIPAddresses11Reservedforexperiments28bits11ClassE~~Reserved21PrivateIPAddressesSpecificrangesofIPaddressessetasideforuseinprivatenetworks(RFC1918)Userestrictedtoprivateinternets;routersinpublicInternetdiscardpacketswiththeseaddressesRange1:to55Range2:to55Range3:to55NetworkAddressTranslation(NAT)usedtoconvertbetweenprivate&globalIPaddresses22ExampleofIPAddressingRNetworkNetworkHHHHHR=routerH=hostInterfaceAddressisInterfaceAddressis50160AddresswithhostID=all0sreferstothenetworkAddresswithhostID=all1sreferstoabroadcastpacket23IPSubnetWhysubnet？MaximHostnumberinA/B/Cdifferentfromeachother;A/B/CclassesNotflexibleSimplifiesmanagementofmultiplicityofLANsSubnetaddressingintroducesanotherhierarchicallevel(e.g.,)HowtosubnetIntradomainonlyTransparenttoremotenetworksChangepartofhostbitstosubnetbits,Introducenetworkmasktoknowhowsubnetwasdoneinside.Tonormalizeusage,treattraditionalA/B/Caddressesasspecialsubnettednetworks(onlyhaveonesubnet)24SubnetAddressingMaskingusedtofindsubnetnumber25Network

MaskIPaddress mask

11001010011101110001011000000101&11111111111111111111111100000000

11001010011101110001011000000000(202)(119)(22)(0)Theresultof(ipandmask)meansnetworkID,soif(address1andmask)equals(address2andmask)meanstheyareinthesamenetworkAllbitsinmaskequals1meansIPaddress’scorrespondingbitsarenetworkpart,0smeanshostpartDefaultMaskforA/B/CaddressA=>B=>C=>26SpecialIPAddressesHostid“all0s”isreservedtorefertoanetworkNumber

(mask),(mask)Hostid“all1s”isreservedtobroadcasttoallhostsonaspecificnetwork

55(mask),55(mask)27SpecialIPAddresses(cont)

isreservedandmeans“unknownaddress“.Normallyusetobootdisklessworkstation55isreservedtobroadcasttoeveryhostonthelocalnetwork127.x.x.xmeans“thisnode”(localloopback).Messagessenttothisaddresswillneverleavethelocalhost.It’spurposeistestingnetworksoftware28IPaddresses:howtogetone?Hosts(hostportion):UsersareassignedIPaddressesbyInternetserviceproviders(ISPs)byhard-codedinsystemDHCP:

DynamicHostConfigurationProtocol:dynamicallygetaddress:“plug-and-play”hostbroadcasts“DHCPdiscover”msgDHCPserverrespondswith“DHCPoffer”msghostrequestsIPaddress:“DHCPrequest”msgDHCPserversendsaddress:“DHCPack”msg29AddressResolutionProtocolH1H2H3H4H1H2H3H4ARPrequest(whatistheMACaddressof2?)ARPresponse(myMACaddressis08:00:5a:3b:94)0123

AlthoughIPaddressidentifiesahost,thepacketisphysicallydeliveredbyanunderlyingnetwork(e.g.,Ethernet)whichusesitsownphysicaladdress(MACaddressinEthernet).HowtomapanIPaddresstoaphysicaladdress?

H1,H2,H3,H4areinthesamenetwork(howtojudge?)H1wantstolearnphysicaladdressofH3->broadcastsanARPrequestEveryhostreceivestherequest,butonlyH3replywithitsphysicaladdress30ExampleofARP31TCP/IPandInternet2TheInternetProtocol2.1IPAddressing2.2IPpacketstructureandtransmission32IPPacketHeaderVersionIHLTypeofServiceTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocolHeaderChecksumSourceIPAddressDestinationIPAddressOptionsPadding04816192431IPheaderTCPheaderHTTPRequest33IPPacketHeaderVersion

IHL

TypeofServiceTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocolHeaderChecksumSourceIPAddressDestinationIPAddressOptionsPadding04816192431Version:currentIPversionis4.Internetheaderlength(IHL):lengthoftheheaderin32-bitwords.Typeofservice(ToS):traditionallypriorityofpacketateachrouter.RecentDifferentiatedServicesredefinesToSfieldtosupportotherservicesthatarebetterthanbesteffort.34IPPacketHeaderVersionIHLTypeofServiceTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocolHeaderChecksumSourceIPAddressDestinationIPAddressOptionsPadding04816192431Totallength:numberofbytesoftheIPpacketincludingheaderanddata,maximumlengthis65535bytes.Identification,Flags,andFragmentOffset:usedforfragmentationandreassembly(Moreonthisshortly).35IPPacketHeaderVersionIHLTypeofServiceTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocolHeaderChecksumSourceIPAddressDestinationIPAddressOptionsPadding04816192431Timetolive(TTL):numberofhopspacketisallowedtotraverseinthenetwork.Eachrouteralongthepathtothedestinationdecrementsthisvaluebyone.Ifthevaluereacheszerobeforethepacketreachesthedestination,therouterdiscardsthepacketandsendsanerrormessagebacktothesource.36IPPacketHeaderVersionIHLTypeofServiceTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocolHeaderChecksumSourceIPAddressDestinationIPAddressOptionsPadding04816192431Protocol:specifiesupper-layerprotocolthatistoreceiveIPdataatthedestination.ExamplesincludeTCP(protocol=6),UDP(protocol=17),andICMP(protocol=1).Headerchecksum:verifiestheintegrityoftheIPheader.(16-bit)SourceIPaddressanddestinationIPaddress:containtheaddressesofthesourceanddestinationhosts.37IPPacketHeaderVersionIHLTypeofServiceTotalLengthIdentificationFlagsFragmentOffsetTimetoLiveProtocolHeaderChecksumSourceIPAddressDestinationIPAddressOptionsPadding04816192431Options:Variablelengthfield,allowspackettorequestspecialfeaturessuchassecuritylevel,routetobetakenbythepacket,andtimestampateachrouter.Detaileddescriptionsoftheseoptionscanbefoundin[RFC791].Padding:Thisfieldisusedtomaketheheaderamultipleof32-bitwords.38ExampleofIPHeader39IPHeaderProcessingatRoutersComputeheaderchecksumforcorrectnessandcheckthatfieldsinheader(e.g.,versionandtotallength)containvalidvaluesConsultroutingtabletodeterminenexthopChangefieldsthatrequireupdating(TTL,headerchecksum)TheIPpacketisthenforwardedalongthenexthop40IPIPRouterSourceDestinationNetworkNetworkFragmentatsourceFragmentatrouterReassembleatdestinationFragmentationandReassemblyMTU:maximumtransmissionunit41FragmentationandReassembly

Identificationidentifiesaparticularpacket,allocatedbysourcehost

Flags=(unused,don’tfragment/DF,morefragment/MF)

Fragmentoffsetidentifiesthelocationofafragmentwithinapacketin64-bitwords42Example:FragmentingaPacketApacketistobeforwardedtoanetworkwithMTUof576bytes.ThepackethasanIPheaderof20bytesandadatapartof1484bytes.andofeachfragment.Maximumdatalengthperfragment=576-20=556bytes.Wesetmaximumdatalengthto552bytestogetmultipleof8.

TotalLengthIdMFFragmentOffsetOriginalpacket1504x00Fragment1572x10Fragment2572x169=552/8Fragment3400x0138=552*2/8Fragmentationinvolvesasubtleperformancepenalty.43Thefragmentsaretobereassembledatdestinationhost.(noreassemblingatrouters)RelievingloadofroutersFragmentsmaygoaheadalongdifferentpathsTimerissetatdestinationhostTimerisstartedoncethefirstfragmentarrivedAllfragmentsofonepacketwillbediscardedifanyoneofthepacketisnotreceivedbeforetimeout.Anderrorinformationwillbereportedtosource.

Fragmentationinvolvesasubtleperformancepenalty.Reassembling44ICMP

(InternetControlMessageProtocol)RFC792;EncapsulatedinIPpacket(protocoltype=1)HandleserrorandcontrolmessagesIfroutercannotdeliverorforwardapacket,itsendsanICMP“hostunreachable”messagetothesourceIfrouterreceivespacketthatshouldhavebeensenttoanotherrouter,itsendsanICMP“redirect”messagetothesender;SendermodifiesitsroutingtableICMP“routerdiscovery”messagesallowhosttolearnaboutroutersinitsnetworkandtoinitializeandupdateitsroutingtablesICMP“echorequestandreply”facilitatediagnosticandusedin“ping”ICMPICMP封裝在IP包內(nèi)（因為ICMP包需要跨越多個路由器）差錯報告功能：向源端報告（不可達(dá)、分組超時、分組頭參數(shù)錯誤），不用于差錯恢復(fù)，僅僅是通告，未規(guī)定后續(xù)處理控制功能：擁塞控制——源抑制報文：請求源端降低發(fā)送速率，未定義恢復(fù)速率報文，源端稍后自動逐步恢復(fù)速率路由重定向：同一網(wǎng)絡(luò)內(nèi)多個路由器，某路由器重定向同網(wǎng)內(nèi)某主機(jī)路由路由器通告（向主機(jī)）、路由器懇求等查詢功能：Echo：ping，tracerouteTimestamp（節(jié)點同步）地址掩碼請求與應(yīng)答2022/11/2NCRL45ICMP2022/11/2NCRL4647TypeCodeChecksumUnusedIPheaderand64bitsoforiginaldatagram081631ICMPBasicErrorMessageFormatTypeandCodeIPheader&64bitsoforiginaldatagramTomatchICMPmessagewithoriginaldatainIPpacket48TypeCodeChecksumIdentifierSequencenumberData081631EchoRequest&EchoReplyMessageFormatEchorequest:type=8;Echoreply:type=0DestinationreplieswithechoreplybycopyingdatainrequestontoreplymessageSequencenumbertomatchreplytorequestIDtodistinguishbetweendifferentsessionsusingechoservicesUsedinPING49Example–Echorequest50Example–EchoReply51TCP/IPandInternet1TheTCP/IPArchitecture2TheInternetProtocol3TransportLayerProtocols:UDPTCP4InternetRouting52OutlineUDPProtocolTCPReliableStreamServiceTCPProtocolTCPConnectionManagementTCPFlowControlTCPCongestionControl53UDPBesteffortdatagramserviceMultiplexingenablessharingofIPdatagramserviceSimpletransmitter&receiverConnectionless:nohandshaking&noconnectionstateLowheaderoverheadNoflowcontrol,noerrorcontrol,nocongestioncontrolUDPdatagramscanbelostorout-of-orderApplicationsmultimedia(e.g.,RTP)networkservices(e.g.,DNS,RIP,SNMP)54UDPDatagramSourceanddestinationportnumbersClientportsareephemeralServerportsarewell-knownMaxnumberis65,535UDPlengthTotalnumberofbytesindatagram(includingheader)8bytes≤length≤65,535UDPChecksumOptionallydetectserrorsinUDPdatagramsourceport#destport#32bitsApplicationdata(message)UDPsegmentformatlengthchecksumLength,inbytesofUDPsegment,includingheader55UDPChecksumCalculationUDPchecksumdetectsforend-to-enderrorsCoverspseudoheaderfollowedbyUDPdatagramIPaddressesincludedtodetectagainstmis-deliveryIP&UDPchecksumssettozeroduringcalculationPadwith1byteofzerosifUDPlengthisodd 00000000Protocol=17UDPLengthSourceIPAddressDestinationIPAddress081631UDPpseudo-header56UDPChecksumCalculation57UDPReceiverChecksumUDPreceiverrecalculatesthechecksumandsilentlydiscardsthedatagramiferrorsdetected“silently”meansnoerrormessageisgeneratedTheuseofUDPchecksumsisoptionalButhostsarerequiredtohavechecksumsenabled58Example59OutlineUDPProtocolTCPReliableStreamServiceTCPProtocolTCPConnectionManagementTCPCongestionControl60TCPReliablebyte-streamserviceMorecomplextransmitter&receiverConnection-oriented:full-duplexunicastconnectionbetweenclient&serverprocessesConnectionsetup,connectionstate,connectionreleaseHigherheaderoverheadErrorcontrol,flowcontrol,andcongestioncontrolHigherdelaythanUDPMostapplicationsuseTCPHTTP,SMTP,FTP,TELNET,POP3,…61ReliableByte-StreamServiceStreamDataTransfertransfersacontiguousstreamofbytesacrossthenetwork,withnoindicationofboundariesgroupsbytesintosegmentstransmitssegmentsasconvenient(Pushfunctiondefined)ReliabilityerrorcontrolmechanismtodealwithIPtransferimpairmentsWrite45bytesWrite15bytesWrite20bytesbufferbufferApplicationTransportRead40bytesRead40bytessegmentsACKS,sequence#ErrorDetection&Retransmission62FlowControlBufferlimitations&speedmismatchcanresultinlossofdatathatarrivesatdestinationReceivercontrolsrateatwhichsendertransmitstopreventbufferoverflowbuffersegmentsbufferusedApplicationTransportadvertisedwindowsize<Bbufferavailable=B63CongestionControlAvailablebandwidthtodestinationvarieswithactivityofotherusersTransmitterdynamicallyadjuststransmissionrateaccordingtonetworkcongestionasindicatedbyRTT(roundtriptime)&ACKsElasticutilizationofnetworkbandwidthbuffersegmentsbufferApplicationTransportACKSRTTEstimation64TCPMultiplexingATCPconnectionisspecifiedbya4-tuple(sourceIPaddress,sourceport,destinationIPaddress,destinationport)TCPallowsmultiplexingofmultipleconnectionsbetweenendsystemstosupportmultipleapplicationssimultaneouslyArrivingsegmentdirectedaccordingtoconnection4-tuple...TCP

IP12m...TCP

IP12nABC...TCP

IP12k(A,5234,B,80)(A,6234,B,80)(C,5234,B,80)65OutlineUDPProtocolTCPReliableStreamServiceTCPProtocolTCPConnectionManagementTCPCongestionControl66TCPProtocol

EachTCPsegmenthasheaderof20ormorebytes+0ormorebytesofdataSourceportDestinationportSequencenumberAcknowledgmentnumberChecksumUrgentpointerOptionsPadding0410162431URGACKPSHRSTSYNFINHeaderlengthReservedWindowsizeDataTCPSegmentFormat67TCPHeaderPortNumbersAsocketidentifiesaconnectionendpointIPaddress+portAconnectionspecifiedbyasocketpairWell-knownportsFTP 21Telnet 23DNS 53HTTP 80Headerlength4bitsLengthofheaderinmultiplesof32-bitwordsMinimumheaderlengthis20bytesMaximumheaderlengthis60bytes68TCPHeaderAcknowledgementNumberSNofnextbyteexpectedbyreceiverAcknowledgesthatallpriorbytesinstreamhavebeenreceivedcorrectlyValidifACKflagissetSequenceNumberBytecountFirstbyteinsegment32bitslong0SN232-1Initialsequencenumberselectedduringconnectionsetup69TCPHeaderReserved6bitsControl6bitsURG:urgentpointerflagUrgentmessageend=SN+urgentpointerACK:ACKpacketflagPSH:overrideTCPbufferingRST:resetconnectionUponreceiptofRST,connectionisterminatedandapplicationlayernotifiedSYN:establishconnectionFIN:closeconnection70TCPHeaderWindowSize16bitstoadvertisewindowsizeUsedforflowcontrolCurrentsenderwillacceptbyteswithSNfromACKtoACK+windowMaximumwindowsizeis65535bytesTCPChecksumInternetchecksummethodTCPpseudoheader+TCPsegment71TCPChecksumCalculationTCPerrordetectionusessameprocedureasUDPTCPpseudo-header00000000Protocol=6TCPsegmentlengthSourceIPaddressDestinationIPaddress08163172OutlineUDPProtocolTCPReliableStreamServiceTCPProtocolTCPConnectionManagementTCPCongestionControl73InitialSequenceNumberSelectinitialsequencenumbers(ISN)toprotectagainstsegmentsfrompriorconnections(thatmaycirculateinthenetworkandarriveatamuchlatertime)SelectISNtoavoidoverlapwithsequencenumbersofpriorconnectionsUselocalclocktoselectISNsequencenumberTimeforclocktogothroughafullcycleshouldbegreaterthanthemaximumlifetimeofasegment(MSL);TypicallyMSL=120secondsHighbandwidthconnectionsposeaproblem2n>2*maxpacketlife*Rbytes/second74TCPConnectionEstablishment“Three-wayHandshake”ISN’sprotectagainstsegmentsfrompriorconnectionsHostAHostBSYN,Seq_no=xSYN,Seq_no=y,ACK,Ack_no=x+1Seq_no=x+1,ACK,Ack_no=y+175IfhostalwaysusesthesameISNHostAHostBSYN,Seq_no=n,ACK,Ack_no=n+1Seq_no=n+1,ACK,Ack_no=n+1DelayedsegmentwithSeq_no=n+2willbeacceptedISNshouldbedifferenteachtimetoavoiddelay,lost,duplicate76MaximumSegmentSizeMaximumSegmentSizelargestblockofdatathatTCPsendstootherendEachendcanannounceitsMSSduringconnectionestablishmentTCPMSSDefaultis536bytesEthernetimpliesMSSof1460bytesIEEE802.3implies145277NearEnd:ConnectionRequest78FarEnd:AckandRequest79NearEnd:Ack80Client-ServerApplicationacceptreturnsread(blocks)readreturnswriteread(blocks)HostA(client)HostB(server)SYN,Seq_no=xSYN,Seq_no=y,ACK,Ack_no=x+1Seq_no=x+1,ACK,Ack_no=y+1socketbindlistenaccept

(blocks)socketconnect(blocks)connectreturnswriteread(blocks)readreturnsRequestmessageReplymessaget1t2t3t4t5t681TCPWindowFlowControl1024bytestotransmit1024bytestotransmit1024bytestotransmit128bytestotransmit1024bytestotransmitcanonlysend512bytesHostAHostBSeq_no=2000,Ack_no=1,Win=1024,Data=2000-3023Seq_no=1,Ack_no=4048,Win=512,Data=1-128Seq_no=3024,Ack_no=1,Win=1024,Data=3024-4047Seq_no=4048,Ack_no=129,Win=1024,Data=4048-4559t1t2t3t4Seq_no=1,Ack_no=2000,Win=2048,NoDatat082“GracefulClose”FIN,seq=5086Ack=5087Data,seq.=303,Ack=5087Deliver150bytesFIN,seq.=453,Ack=5087Ack=454HostAHostBAck=453TCPConnectionClosingTerminatingABTerminatingBA835.3TCPcongestioncontrolTCPusesaslidingwindowprotocolforendtoendflowcontrol.Theadvertisedwindowensuresthatthereceiver’sbufferwillneveroverflow,doesnotpreventthebuffersintheintermediateroutersformoverflowing.IPlayerdoesnotamechanismtoco