TCP/IPBasics

(ProtocolsandtheTCP/IPSuite)TCP:TransmissionControlProtocol

IP:InternetProtocol1精選課件Multi-layerCommunication(1/2)2精選課件Multi-layerCommunication(2/2)Aseriesoflayers,eachbuiltupontheonebelowit.Thepurposeofeachlayeristooffercertainservicestohigherlayers,hidingthedetailedimplementationoftheseservicesfromhigherlayersEachlayeriscompletelyindependentofothersaslongastheinterfacesarenotchanged.Sothesecretariescanswitchfromfaxtoemail,withoutdisturbingotherlayers3精選課件ProtocolProtocolisanagreementbetweentwocommunicationpartiesonhowcommunicationistoproceedTwocommunicationpartiescommunicatebymeansofformattedblocksofdatathatobeytherulesandconventionsknownasaprotocolKeyfeaturesofaprotocolSyntax:ConcernstheformatofthedatablocksSemantics:IncludescontrolinformationforcoordinationanderrorhandlingTiming:Includesspeedmatchingandsequencing4精選課件AgentsInvolvedinCommunicationApplicationsExchangedatabetweencomputers(e.g.,electronicmail)ComputersConnectedtonetworksNetworksTransfersdatafromonecomputertoanother5精選課件TCP/IPLayersCommunicationtaskisorganizedintofiverelativelyindependentlayersPhysicallayer…Layer1Networkaccesslayer…Layer2Internetlayer…Layer3Host-to-host(end-to-end),

ortransportlayerApplicationlayer(serviceaccesspoint)6精選課件LayeredConcepts7精選課件Physical(PHY)LayerCoversthephysicalinterfacebetweena

transmissiondevice(e.g.,workstation,

computer)andatransmissionmediumornetworkThesendingcomputermustprovidethenetworkoftheaddressofthedestinationcomputerThesendingcomputermaywishtoinvokecertainservicesprovidedbythenetworkDifferentstandardshavebeendevelopedPhysicallayerspecifies:CharacteristicsofthetransmissionmediumThenatureofsignalsDatarateOtherrelatedmattersUpperlayersabovenetworkaccessdonotneedtoconsiderthespecificsofthenetworktobeused8精選課件NetworkAccessLayerConcernedwiththeexchangeofdatabetween

anendsystem(server,workstation)andthenetworktowhichitisattachedSoftwareuseddependsontypeofnetworkCircuitswitchingPacketswitching(e.g.,X.25)LANs(e.g.,Ethernet)Others9精選課件InternetLayerNetworkaccesslayerisconcernedwith

accessandroutingdataacrossanetworkfor

twoendsystemsattachedthesamenetworkUsestheInternetprotocol(IP)whendevicesareattachedtodifferentnetworksProvidesroutingfunctionstoallowdatatotraversemultipleinterconnectednetworksImplementedinendsystemsandroutersArouterisaprocessororhostthatconnectstwonetworks.Themainfunctionistorelaydatafromonenetworktotheotheronitsroutefromthesourcetothedestinationendsystems10精選課件Host-to-Host,orTransportLayerProvidesreliabilityduringdataexchangesCompletenessOrder(Ifanapplicationneedstoexchangedatabetweentwocomputers,wealwayshopethedatawouldbetransmittedreliably.Allthedataarriveatthedestinationcorrectlyandarriveasthesameorderinwhichtheyweresentonthesourceapplication.)TransmissionControlProtocol(TCP)iscommonlyused另一種協(xié)定是UDP(UserDatagramProtocol)11精選課件Host-to-Host,orTransportLayer—TCPConnection-orientedprotocolProvidesareliableunicastend-to-endbytestreamoveranunreliableinternetwork.12精選課件Host-to-Host,orTransportLayer—Connection-OrientedBeforeanydatatransfer,TCPestablishesaconnection(3-wayhandshake)OneTCPentityiswaitingforaconnection(“server”)TheotherTCPentity(“client”)contactstheserverEachconnectionisfullduplex13精選課件Host-to-Host,orTransportLayer—ReliableBytestreamisbrokenupintochunks,i.e.,segmentsReceiversendsacknowledgements(ACKs)forsegmentsTCPmaintainsatimer.IfanACKisnotreceivedintime, thesegmentisretransmittedDetectingerrorsTCPhaschecksumsforheaderanddata.SegmentswithinvalidchecksumsarediscardedEachbytethatistransmittedhasasequencenumber14精選課件ByteStreamServiceTothelowerlayers,TCPhandlesdatainblocks(segments)TothehigherlayersTCPhandlesdataasasequenceofbytesanddoesnotidentifyboundariesbetweenbytesHigherlayersdonotknowaboutthebeginningandendofsegments15精選課件ApplicationLayerContainsthelogicneededtosupportvarious

userapplicationsUsesseparatemodulesthatarepeculiartoeachdifferenttypeofapplicationE.g.,e-mail,FTP,WWW,…16精選課件OperationsofTCPandIPTotalcommunicationsfacilitymayconsistofmultiplenetworksTheconstituentnetworks—subnetworksNetworkaccessprotocolIPImplementedinbothendsystemsandroutersRouteablockofdatafromoneendsystem,throughoneormorerouters,toanotherendsystemTCPOnlyimplementedintheendsystemsKeepstrackoftheblocksofdatatomakesurethatallaredeliveredreliablytotheappropriateapplication17精選課件OperationsofTCPandIPTwolevelsofaddressEachhostonasubnetworkmusthaveaglobalInternetaddress(e.g.,140.125.xxx.yyy)Eachprocesswithahostmusthaveanaddressthatisuniquewithinthehost—portsAportnumberidentifiestheendpointofaconnection.Pairs<clientIPaddr.,serverport#>and<serverIPaddr.,serverport#>identifyaTCPconnection.18精選課件TraceaSimpleOperation(1/2)36819精選課件TraceaSimpleOperation(2/2)Supposeoneapplication,associatedwith

port1inhostA,wishestosenddatato

anotherapplication,whichhasportnumber3inhostB.TheapplicationatAhandsthemessagedowntoTCPwithinstructiontosendittoports3athostB.TCPhandsthemessagedowntoIPwithinstructiontosendittohostB.IPneedsnottobetoldtheidentityofthedestinationport.AllitneedstoknowisthatthedataisintendedtohostB.IPhandsthemessagedowntonetworkaccesslayerwiththeinstructionstosendthemessagetorouterJ.ThesendingapplicationgeneratesblocksofdataandpassesittoTCP.TCPappendscontrolinformation,i.e.,TCPheader.ThecontrolinformationisusedatthepeerTCPprotocolathostB.20精選課件RefertoRFC(RequestforComments)793DestinationportSequencenumberChecksumCodebitsFIN:結(jié)束連線SYN:建立連線RST:重置連線PSH:封包立即傳送ACK:回應(yīng)上一次收到

的封包URG:請(qǐng)接收端立即處

理此封包(urgent)TCPHeader21精選課件TCPHeaderEachsequencenumberidentifiesabyte

inthebytestreamAcknowledgementNumber(AckNo)AcknowledgementsarepiggybackedAsegmentfromA→BcancontainanacknowledgementforadatasentintheB→AdirectionAhostusesAckNotosendacknowledgements.(IfahostsendsanAckNoinasegmentitsetsthe“ACKflag”)AckNocontainsthenextSeqNothatahostwantstoreceive例:Theacknowledgementforasegmentwithsequencenumbers0-1500isAckNo=1501例:Sendersendstwosegmentswith“1..1500”and“1501..3000”,butreceiveronlygetsthesecondsegment.Inthiscase,thereceivercannotacknowledgethesecondpacket.ItcanonlysendAckNo=122精選課件TCPConnectionEstablishmentTCPusesathree-way

handshaketoopena

connection:(1)ClientsendsasegmentwithSYNbitsetportnumberofclientinitialsequencenumber(ISN)ofclient(2)ServerrespondswithasegmentwithSYNbitsetinitialsequencenumberofserverACKforISNofclient(3)ClientacknowledgesbysendingasegmentwithACKISNofserver23精選課件ProtocolDataUnits(PDUs)AblockofinformationexchangedatanyprotocollevelisreferredtoasPDUsHeader+Data(payload)

+TrailerDestinationPortSequencenumberChecksumDestination

IPAddressSourceIPaddressDest.NetworkAddressPriorityinfo24精選課件IPDatagramFormat25精選課件IPDatagramFormat:FieldsoftheHeader(1/4)Version(4bits):currentversionis4,nextversion6Headerlength(4bits):lengthofIPheader,inmultiplesof4bytesDS/ECNfield(1byte)ThisfieldwaspreviouslycalledasType-of-Service(TOS)field.Theroleofthisfieldhasbeenre-defined,butis“backwardscompatible”toTOSinterpretationDifferentiatedService(DS)(6bits):Usedtospecifyservicelevel(currentlynotsupportedintheInternet)ExplicitCongestionNotification(ECN)(2bits):NewfeedbackmechanismusedbyTCP26精選課件IPDatagramFormat:FieldsoftheHeader(2/4)Identification(16bits)UniqueidentificationofadatagramfromahostIncrementedwheneveradatagramistransmittedFlags(3bits)Firstbitalwayssetto0DFbit(Donotfragment)MFbit(Morefragments)TimeToLive(TTL)(1byte)

SpecifieslongestpathsbeforedatagramisdroppedRoleofTTLfield:EnsurethatpacketiseventuallydroppedwhenaroutingloopoccursUsedasfollows:Sendersetsthevalue(e.g.,64)Eachrouterdecrementsthevalueby1Whenthevaluereaches0,thedatagramisdropped27精選課件Protocol(1byte)Specifiesthehigher-layerprotocolUsedfordemultiplexingtohigherlayersHeaderchecksum(2bytes)Asimple16-bitlongchecksumwhichiscomputedfortheheaderofthedatagramIPDatagramFormat:FieldsoftheHeader(3/4)28精選課件IPDatagramFormat:FieldsoftheHeader(4/4)OptionsSecurityrestrictionsRecordRoute:eachrouterthatprocessesthepacketaddsitsIPaddresstotheheaderTimestamp:eachrouterthatprocessesthepacketaddsitsIPaddressandtimetotheheader(loose)SourceRouting:specifiesalistofroutersthatmustbetraversed(strict)SourceRouting:specifiesalistoftheonlyroutersthatcanbetraversedPaddingPaddingbytesareaddedtoensurethatheaderendsona4-byteboundary29精選課件CommonTCP/IPApplicationsApplicationsthathavebeenstandardizedtooperateoverTCPinclude:Simplemailtransferprotocol(SMTP):providesabasicelectronicmailfacilityFileTransferProtocol(FTP):allowsfilestobesentfromonesystemtoanotherTELNET:Providesaremotelogoncapability…30精選課件SomeProtocolsinTCP/IPSuite31精選課件LayersoftheOSIModelTheOSI(OpenSystemsInterconnection)referencewasdevelopedbytheInternationalOrganizationforStandardization(ISO)ApplicationPresentationSessionTransportNetworkDatalinkPhysical32精選課件LayersoftheOSIModelApplicationlayerProvidesaccesstotheOSIenvironmentforusersProvidesdistributedinformationservicesPresentationlayerProvidesindependencetotheapplicationprocessesfromdifferencesindatarepresentation(syntax)Concernedwiththesyntaxandsemanticsoftheinformationtransmitted,e.g.ACSIIcode,UnicodeincompatibleDatacompressionEncryption33精選課件LayersoftheOSIModelSessionlayerProvidesthecontrolstructureforcommunication

betweenapplicationsWhoseturntotalk?Establishes,manages,andterminatesconnectionsbetweencooperatingapplicationsTokenmanagement:dialoguediscipline(full-duplex,half-duplex)Forsomeprotocols,itisessentialthatbothsidesdonotattemptthesameoperationatthesametime.OnlythesideholdingthetokenmayperformthecriticaloperationSynchronizationInsertcheckpointsintothedatastream,sothatafteracrash,onlythedatatransferredafterthelastcheckpointneedtoberepeated34精選課件LayersoftheOSIModelTransportlayerProvidesreliable,transparenttransferofdatabetween

endpointsProvidesend-to-enderrorrecoveryandflowcontrolNetworklayerProvidesupperlayerswithindependencefromthedatatransmissionandswitchingtechnologiesusedtoconnectsystemsResponsibleforestablishing,maintaining,andterminatingconnectionsAkeydesignissueisdetermininghowpacketsareroutedfromsourcetodestination.Statictable?Dynamictableisdeterminedanewforeachpacket,toreflectthecurrentnetworkload35精選課件LayersoftheOSIModelData-linklayerProvidesthereliabletransferofinformationacross

thephysicallinkSendsblocks(frames)withthenecessarysynchronization,errorcontrol(errordetection/correction),andflowcontrolPhysicallayerTransmissionofunstructuredbitstreamoverphysicalmediumDealswithaccessingthephysicalmediumMechanicalcharacteristicsElectricalcharacteristicsFunctionalcharacteristicsProceduralcharacteristics36精選課件ComparisonofOSIandTCP/IP37精選課件TCP/IPArchitecturalDominanceTCP/IPprotocolsmaturedquickerthansimilarOSIprotocolsWhentheneedforinteroperabilityacrossnetworkswasrecognized,onlyTCP/IPwasavailableandreadytogoOSImodelisunnecessarilycomplexAccomplishesinsevenlayerswhatTCP/IPdoeswithfewerlayers38精選課件InternetworkingTerms(名詞)Communicationnetwork–facilitythatprovidesadatatransferserviceamongdevicesattachedtothenetworkInternet–collectionofcommunicationnetworks,interconnectedbybridges/routersIntranet–internetusedbyanorganizationforinternalpurposesProvideskeyInternetapplicationsCanexistasanisolated,self-containedinternetInmostcases,aLANorWANisnotisolated.Forexample,anorganizationmayhavemorethanonetypeofLANsatdifferentsites,andneedthemtobeinterconnectedviaWANsforcentralcontrolofdistributedinformationexchange.39精選課件InternetworkingTerms(cont’d)EndSystem(ES)–deviceusedtosupportend-userapplicationsorservicesIntermediateSystem(IS)–deviceusedtoconnecttwonetworksEachsubnetworkinaninternetsupportscommunicationamongthedevicesattachedtothatsubnetwork.Subnetworksareconnec