Chapter-2-Application-Layer-高級(jí)計(jì)算機(jī)網(wǎng)絡(luò)-教學(xué)課件(英文版)

Chapter2

ApplicationLayerComputerNetworking:ATopDownApproach,

4thedition.

JimKurose,KeithRoss

Addison-Wesley,July2007.

12:ApplicationLayerChapter2

ApplicationLayerComChapter2:Applicationlayer2.1Principlesofnetworkapplications2.2WebandHTTP2.3FTP2.4ElectronicMailSMTP,POP3,IMAP2.5DNS2.6P2Papplications2.7SocketprogrammingwithTCP2.8SocketprogrammingwithUDP22:ApplicationLayerChapter2:Applicationlayer2.Chapter2:ApplicationLayerOurgoals:

conceptual,implementationaspectsofnetworkapplicationprotocolstransport-layerservicemodelsclient-serverparadigmpeer-to-peerparadigmlearnaboutprotocolsbyexaminingpopularapplication-levelprotocolsHTTPFTPSMTP/POP3/IMAPDNSprogrammingnetworkapplicationssocketAPI32:ApplicationLayerChapter2:ApplicationLayerOuSomenetworkappse-mailwebinstantmessagingremoteloginP2Pfilesharingmulti-usernetworkgamesstreamingstoredvideoclipsvoiceoverIPreal-timevideoconferencinggridcomputing

42:ApplicationLayerSomenetworkappse-mailvoiceoCreatinganetworkappwriteprogramsthatrunon(different)endsystemscommunicateovernetworke.g.,webserversoftwarecommunicateswithbrowsersoftwareNoneedtowritesoftwarefornetwork-coredevicesNetwork-coredevicesdonotrunuserapplicationsapplicationsonendsystemsallowsforrapidappdevelopment,propagationapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysicalapplicationtransportnetworkdatalinkphysical52:ApplicationLayerCreatinganetworkappwriteprChapter2:Applicationlayer2.1Principlesofnetworkapplications2.2WebandHTTP2.3FTP2.4ElectronicMailSMTP,POP3,IMAP2.5DNS2.6P2Papplications2.7SocketprogrammingwithTCP2.8SocketprogrammingwithUDP2.9BuildingaWebserver62:ApplicationLayerChapter2:Applicationlayer2.ApplicationarchitecturesClient-serverPeer-to-peer(P2P)Hybridofclient-serverandP2P72:ApplicationLayerApplicationarchitecturesClienClient-serverarchitectureserver:

always-onhostpermanentIPaddressserverfarmsforscaling主機(jī)群集clients:communicatewithservermaybeintermittentlyconnectedmayhavedynamicIPaddressesdonotcommunicatedirectlywitheachotherclient/server82:ApplicationLayerClient-serverarchitectureservPureP2Parchitecturenoalways-onserverarbitraryendsystemsdirectlycommunicatepeersareintermittentlyconnectedandchangeIPaddressesHighlyscalablebutdifficulttomanagepeer-peer92:ApplicationLayerPureP2ParchitecturenoalwaysHybridofclient-serverandP2PSkypevoice-over-IPP2Papplicationcentralizedservice:clientpresencedetection/locationuserregistersitsIPaddresswithcentralserverwhenitcomesonlineusercontactscentralservertofindIPaddressesofbuddiesclient-clientconnection:direct(notthroughserver),chattingbetweentwousersisP2PInstantmessagingMSN,QQ,102:ApplicationLayerHybridofclient-serverandP2112:ApplicationLayer112:ApplicationLayerProcessescommunicatingProcess:programrunningwithinahost.withinsamehost,twoprocessescommunicateusinginter-processcommunication(definedbyOS).processesindifferenthostscommunicatebyexchangingmessagesClientprocess:processthatinitiatescommunicationServerprocess:processthatwaitstobecontactedNote:applicationswithP2Parchitectureshaveclientprocesses&serverprocesses122:ApplicationLayerProcessescommunicatingProcessSocketsprocesssends/receivesmessagesto/fromitssocketsocketanalogoustodoordefinitionAsocketisoneendpointofatwo-waycommunicationlinkbetweentwoprogramsrunningonthenetwork.AsocketisboundtoaportnumbersothattheTCPlayercanidentifytheapplicationthatdataisdestinedtobesent.

processTCPwithbuffers,variablessockethostorserverprocessTCPwithbuffers,variablessockethostorserverInternetcontrolledbyOScontrolledbyappdeveloperAPI(ApplicationProgrammingInterface):(1)choiceoftransportprotocol;(2)abilitytofixafewparameters(lotsmoreonthislater)

132:ApplicationLayerSocketsprocesssends/receivesAnendpointisacombinationofanIPaddressandaportnumber.EveryTCPconnectioncanbeuniquelyidentifiedbyitstwoendpoints.Thatwayyoucanhavemultipleconnectionsbetweenyourhostandtheserver.<source-portnumber,s-IPaddress,destination-portnumber,d-IPaddress>142:ApplicationLayerAnendpointisacombinationoOntheclient-side:Tomakeaconnectionrequest,theclienttriestorendezvous（在指定地點(diǎn)集合）withtheserverontheserver'smachineandport.Theclientalsoneedstoidentifyitselftotheserversoitbindstoalocalportnumberthatitwilluseduringthisconnection.Thisisusuallyassignedbythesystem.152:ApplicationLayerOntheclient-side:TomakeaNormally,aserverrunsonaspecificcomputerandhasasocketthatisboundtoaspecificportnumber.Theserverjustwaits,listeningtothesocketforaclienttomakeaconnectionrequest.Ontheserver-side:Ifeverythinggoeswell,theserveracceptstheconnection.Uponacceptance,theservergetsanewsocketboundtothesamelocalportandalsohasitsremoteendpointsettotheaddressandportoftheclient.Itneedsanewsocketsothatitcancontinuetolistentotheoriginalsocketforconnectionrequestswhiletendingtotheneedsoftheconnectedclient.162:ApplicationLayerNormally,aserverrunsonasAddressingprocessestoreceivemessages,processmusthaveidentifierhostdevicehasunique32-bitIPaddressQ:doesIPaddressofhostsufficeforidentifyingtheprocess?172:ApplicationLayerAddressingprocessestoreceiveAddressingprocessestoreceivemessages,processmusthaveidentifierhostdevicehasunique32-bitIPaddressQ:doesIPaddressofhostonwhichprocessrunssufficeforidentifyingtheprocess?A:No,manyprocessescanberunningonsamehostidentifier

includesbothIPaddressandportnumbersassociatedwithprocessonhost.Exampleportnumbers:HTTPserver:80Mailserver:25tosendHTTPmessagetowebserver:IPaddress:

2Portnumber:

80182:ApplicationLayerAddressingprocessestoreceiveApp-layerprotocoldefinesTypesofmessagesexchanged,e.g.,request,responseMessagesyntax:whatfieldsinmessages&howfieldsaredelineatedMessagesemantics

meaningofinformationinfieldsRulesforwhenandhowprocessessend&respondtomessagesPublic-domainprotocols:definedinRFCsallowsforinteroperabilitye.g.,HTTP,SMTPProprietaryprotocols:e.g.,Skype192:ApplicationLayerApp-layerprotocoldefinesTypeWhattransportservicedoesanappneed?Datalosssomeapps(e.g.,audio)cantoleratesomelossotherapps(e.g.,filetransfer,telnet)require100%reliabledatatransfer

Timingsomeapps(e.g.,Internettelephony,interactivegames)requirelowdelaytobe“effective”Throughputsomeapps(e.g.,multimedia)requireminimumamountofthroughputtobe“effective”otherapps(“elasticapps”)makeuseofwhateverthroughputtheygetSecurityEncryption,dataintegrity,…202:ApplicationLayerWhattransportservicedoesanTransportservicerequirementsofcommonappsApplicationfiletransfere-mailWebdocumentsreal-timeaudio/videostoredaudio/videointeractivegamesinstantmessagingDatalossnolossnolossnolossloss-tolerantloss-tolerantloss-tolerantnolossThroughputelasticelasticelasticaudio:5kbps-1Mbpsvideo:10kbps-5MbpssameasabovefewkbpsupelasticTimeSensitivenononoyes,100’smsecyes,fewsecsyes,100’smsecyesandno212:ApplicationLayerTransportservicerequirementsInternettransportprotocolsservicesTCPservice:connection-oriented:setuprequiredbetweenclientandserverprocessesreliabletransportbetweensendingandreceivingprocessflowcontrol:senderwon’toverwhelmreceivercongestioncontrol:throttlesenderwhennetworkoverloadeddoesnotprovide:timing,minimumthroughputguarantees,securityUDPservice:unreliabledatatransferbetweensendingandreceivingprocessdoesnotprovide:connectionsetup,reliability,flowcontrol,congestioncontrol,timing,throughputguarantee,orsecurityQ:whybother?WhyisthereaUDP?222:ApplicationLayerInternettransportprotocolssInternetapps:application,transportprotocolsApplicatione-mailremoteterminalaccessWebfiletransferstreamingmultimediaInternettelephonyApplicationlayerprotocolSMTP[RFC2821]Telnet[RFC854]HTTP[RFC2616]FTP[RFC959]HTTP(egYoutube),

RTP[RFC1889]SIP,RTP,proprietary(e.g.,Skype)UnderlyingtransportprotocolTCPTCPTCPTCPTCPorUDPtypicallyUDP232:ApplicationLayerInternetapps:application,tSIP-SessionInitiationProtocol-isanetworkcommunicationsprotocolcommonlyemployedforVoiceoverIPsignaling.RTP-(RealtimeTransportProtocol)-AnIPprotocolthatsupportsreal-timetransmissionofvoiceandvideo.ItiswidelyusedforIPtelephonyandaudioandvideostreaming.AnRTPpacketridesontopofUDPandincludestimestampingandsynchronizationinformationinitsheaderforproperreassemblyatthereceivingend.SecureRTP(SRTP)isaversionofRTPthatprovidesconfidentialityandmessageauthentication.

242:ApplicationLayerSIP-SessionInitiationProtoChapter2:Applicationlayer2.1Principlesofnetworkapplicationsapparchitecturesapprequirements2.2WebandHTTP2.4ElectronicMailSMTP,POP3,IMAP2.5DNS2.6P2Papplications2.7SocketprogrammingwithTCP2.8SocketprogrammingwithUDP252:ApplicationLayerChapter2:Applicationlayer2.WebandHTTPFirstsomejargon（行話）Webisakindofapplication.WebpageconsistsofobjectsObjectcanbeHTMLfile,JPEGimage,Javaapplet,audiofile,…WebpageconsistsofbaseHTML-filewhichincludesseveralreferencedobjectsEachobjectisaddressablebyaURL/someDept/pic.gifhostnamepathname262:ApplicationLayerWebandHTTPFirstsomejargon（HTTPoverviewHTTP:hypertexttransferprotocolWeb’sapplicationlayerprotocolclient/servermodelclient:browserthatrequests,receives,“displays”Webobjectsserver:WebserversendsobjectsinresponsetorequestsPCrunningExplorerServerrunningApacheWebserverMacrunningNavigatorHTTPrequestHTTPrequestHTTPresponseHTTPresponse272:ApplicationLayerHTTPoverviewHTTP:hypertexttHTTPoverview(continued)UsesTCP:clientinitiatesTCPconnection(createssocket)toserver,port80serveracceptsTCPconnectionfromclientHTTPmessages(application-layerprotocolmessages)exchangedbetweenbrowser(HTTPclient)andWebserver(HTTPserver)TCPconnectionclosedHTTPis“stateless”servermaintainsnoinformationaboutpastclientrequestsProtocolsthatmaintain“state”arecomplex!pasthistory(state)mustbemaintainedifserver/clientcrashes,theirviewsof“state”maybeinconsistent,mustbereconciledaside282:ApplicationLayerHTTPoverview(continued)UsesHTTPconnectionsNonpersistentHTTP非持久AtmostoneobjectissentoveraTCPconnection.PersistentHTTPMultipleobjectscanbesentoversingleTCPconnectionbetweenclientandserver.292:ApplicationLayerHTTPconnectionsNonpersistentNonpersistentHTTPSupposeuserentersURLwww.someS/someDepartment/home.index1a.HTTPclientinitiatesTCPconnectiontoHTTPserver(process)atwww.someSonport802.HTTPclientsendsHTTPrequestmessage(containingURL)intoTCPconnectionsocket.MessageindicatesthatclientwantsobjectsomeDepartment/home.index1b.HTTPserverathostwww.someSwaitingforTCPconnectionatport80.“accepts”connection,notifyingclient3.HTTPserverreceivesrequestmessage,formsresponsemessagecontainingrequestedobject,andsendsmessageintoitssockettime(containstext,referencesto10jpegimages)302:ApplicationLayerNonpersistentHTTPSupposeuserNonpersistentHTTP(cont.)5.HTTPclientreceivesresponsemessagecontaininghtmlfile,displayshtml.Parsinghtmlfile,finds10referencedjpegobjects6.

Steps1-5repeatedforeachof10jpegobjects4.HTTPserverclosesTCPconnection.time312:ApplicationLayerNonpersistentHTTP(cont.)5.HNon-PersistentHTTP:ResponsetimeDefinitionofRTT:timeforasmallpackettotravelfromclienttoserverandback.Responsetime:oneRTTtoinitiateTCPconnectiononeRTTforHTTPrequestandfirstfewbytesofHTTPresponsetoreturnfiletransmissiontimetotal=2RTT+transmittimetimetotransmitfileinitiateTCPconnectionRTTrequestfileRTTfilereceivedtimetime322:ApplicationLayerNon-PersistentHTTP:ResponsePersistentHTTPNonpersistentHTTPissues:requires2RTTsperobjectOSoverheadforeachTCPconnectionbrowsersoftenopenparallelTCPconnectionstofetchreferencedobjectsPersistentHTTPserverleavesconnectionopenaftersendingresponsesubsequentHTTPmessagesbetweensameclient/serversentoveropenconnectionclientsendsrequestsassoonasitencountersareferencedobjectaslittleasoneRTTforallthereferencedobjects332:ApplicationLayerPersistentHTTPNonpersistentHHTTPrequestmessagetwotypesofHTTPmessages:request,responseHTTPrequestmessage:ASCII(human-readableformat)GET/somedir/page.htmlHTTP/1.1Host:User-agent:Mozilla/4.0Connection:closeAccept-language:fr(extracarriagereturn,linefeed)

requestline(GET,POST,HEADcommands)headerlinesCarriagereturn,linefeedindicatesendofmessage342:ApplicationLayerHTTPrequestmessagetwotypesHTTPrequestmessage:generalformat352:ApplicationLayerHTTPrequestmessage:generalUploadingforminputPostmethod:WebpageoftenincludesforminputInputisuploadedtoserverinentitybodyURLmethod:UsesGETmethodInputisuploadedinURLfieldofrequestline:/animalsearch?monkeys&banana362:ApplicationLayerUploadingforminputPostmetho372:ApplicationLayer372:ApplicationLayerzh-cn:simplifiedchinese

Accept-Encoding:gzip,deflate

User-Agent:Mozilla/4.0(compatible;MSIE6.0;WindowsNT5.1;SV1;InfoPath.1;.NETCLR2.0.50727)

theieoftheuser382:ApplicationLayerzh-cn:simplifiedchinese382:MethodtypesHTTP/1.0GETPOSTHEADasksservertoleaverequestedobjectoutofresponseUsedtotracefaultsHTTP/1.1GET,POST,HEADPUTuploadsfileinentitybodytopathspecifiedinURLfieldDELETEdeletesfilespecifiedintheURLfield392:ApplicationLayerMethodtypesHTTP/1.0HTTP/1.139HTTPresponsemessageHTTP/1.1200OKConnectioncloseDate:Thu,06Aug199812:00:15GMTServer:Apache/1.3.0(Unix)Last-Modified:Mon,22Jun1998…...Content-Length:6821Content-Type:text/html

datadatadatadatadata...statusline(protocolstatuscodestatusphrase)headerlinesdata,e.g.,requestedHTMLfile402:ApplicationLayerHTTPresponsemessageHTTP/1.1412:ApplicationLayer412:ApplicationLayerHTTPresponsestatuscodes200OKrequestsucceeded,requestedobjectlaterinthismessage301MovedPermanentlyrequestedobjectmoved,newlocationspecifiedlaterinthismessage(Location:)400BadRequestrequestmessagenotunderstoodbyserver404NotFoundrequesteddocumentnotfoundonthisserver505HTTPVersionNotSupportedInfirstlineinserver->clientresponsemessage.Afewsamplecodes:422:ApplicationLayerHTTPresponsestatuscodes200TryingoutHTTP(clientside)foryourselfOpenethereal;Stopcapture432:ApplicationLayerTryingoutHTTP(clientside)User-serverstate:cookiesManymajorWebsitesusecookiesFourcomponents:1)cookieheaderlineofHTTPresponsemessage2)cookieheaderlineinHTTPrequestmessage3)cookiefilekeptonuser’shost,managedbyuser’sbrowser4)back-enddatabaseatWebsiteExample:SusanalwaysaccessInternetalwaysfromPCvisitsspecifice-commercesiteforfirsttimewheninitialHTTPrequestsarrivesatsite,sitecreates:uniqueIDentryinbackenddatabaseforID442:ApplicationLayerUser-serverstate:cookiesManyCookies:keeping“state”(cont.)clientserverusualhttpresponsemsgusualhttpresponsemsgcookiefileoneweeklater:usualhttprequestmsgcookie:1678cookie-specificactionaccessebay8734usualhttprequestmsgAmazonservercreatesID1678forusercreateentryusualhttpresponseSet-cookie:1678ebay8734amazon1678usualhttprequestmsgcookie:1678cookie-spectificactionaccessebay8734amazon1678backenddatabase452:ApplicationLayerCookies:keeping“state”(contCookies(continued)Whatcookiescanbring:authorizationshoppingcardsrecommendationsusersessionstate(Webe-mail)Cookiesandprivacy:cookiespermitsitestolearnalotaboutyouyoumaysupplynameande-mailtositesasideHowtokeep“state”:protocolendpoints:maintainstateatsender/receiverovermultipletransactionscookies:httpmessagescarrystate462:ApplicationLayerCookies(continued)WhatcookieXP:C:\DocumentsandSettings\Administrator\Cookiesvista：C:/users/用戶名/AppData/Roaming/Microsoft/windows/cokies472:ApplicationLayerXP:C:\DocumentsandSettiWebcaches(proxyserver)usersetsbrowser:WebaccessesviacachebrowsersendsallHTTPrequeststocacheobjectincache:cachereturnsobjectelsecacherequestsobjectfromoriginserver,thenreturnsobjecttoclientGoal:satisfyclientrequestwithoutinvolvingoriginserverclientProxyserverclientHTTPrequestHTTPresponseHTTPrequestHTTPrequestoriginserveroriginserverHTTPresponseHTTPresponse482:ApplicationLayerWebcaches(proxyserver)userMoreaboutWebcachingcacheactsasbothclientandservertypicallycacheisinstalledbyISP(university,company,residentialISP)WhyWebcaching?reduceresponsetimeforclientrequestreducetrafficonaninstitution’saccesslink.Internetdensewithcaches:enables“poor”contentproviderstoeffectivelydelivercontent(butsodoesP2Pfilesharing)492:ApplicationLayerMoreaboutWebcachingcacheacCachingexampleAssumptionsaverageobjectsize=100,000bitsavg.requestratefrominstitution’sbrowserstooriginservers=15/secdelayfrominstitutionalroutertoanyoriginserverandbacktorouter=2secoriginserverspublicInternetinstitutionalnetwork10MbpsLAN1.5Mbpsaccesslinkinstitutionalcache502:ApplicationLayerCachingexampleAssumptionsoriConsequencesutilizationonLAN=15/sec*100,000bits/10Mbps=15*100,000/10000,000=0.15utilizationonaccesslink=15/sec*100,000bits/1.5Mbps=1500,000/1500,000=1totaldelay=Internetdelay+accessdelay+LANdelay=2sec+minutes+millisecondsoriginserverspublicInternetinstitutionalnetwork10MbpsLAN1.5Mbpsaccesslinkinstitutionalcache512:ApplicationLayerConsequencesoriginpublicinstitCachingexample(cont)possiblesolution1increasebandwidthofaccesslinkto,say,10MbpsconsequenceutilizationonLAN=15%utilizationonaccesslink=

15/sec*100,000bits/1.5Mbps=1,500,000/10,000,000=

15%Totaldelay=Internetdelay+accessdelay+LANdelay=2sec+msecs+msecsoftenacostlyupgradeoriginserverspublicInternetinstitutionalnetwork10MbpsLAN10Mbpsaccesslinkinstitutionalcache522:ApplicationLayerCachingexample(cont)possibleCachingexample(cont)possiblesolution2:installcachesupposehitrateis0.4consequence40%requestswillbesatisfiedalmostimmediately60%requestssatisfiedbyoriginserverutilizationofaccesslinkreducedto60%,resultinginnegligibledelays(say10msec)totalavgdelay=Internetdelay+accessdelay+LANdelay=0.6*(2.01)secs+0.4*(0.01)secs<1.4secsoriginserverspublicInternetinstitutionalnetwork10MbpsLAN1.5Mbpsaccesslinkinstitutionalcache532:ApplicationLayerCachingexample(cont)possibleConditionalGETGoal:don’tsendobjectifcachehasup-to-datecachedversioncache:specifydateofcachedcopyinHTTPrequestIf-modified-since:<date>server:responsecontainsnoobjectifcachedcopyisup-to-date:HTTP/1.0304NotModifiedcacheserverHTTPrequestmsgIf-modified-since:<date>HTTPresponseHTTP/1.0304NotModifiedobjectnotmodifiedHTTPrequestmsgIf-modified-since:<date>HTTPresponseHTTP/1.0200OK<data>objectmodified542:ApplicationLayerConditionalGETGoal:don’tsenChapter2:Applicationlayer2.1Principlesofnetworkapplications2.2WebandHTTP2.3FTP

2.4ElectronicMailSMTP,POP3,IMAP2.5DNS2.6P2Papplications2.7SocketprogrammingwithTCP2.8SocketprogrammingwithUDP2.9BuildingaWebserver552:ApplicationLayerChapter2:Applicationlayer2.FTP:thefiletransferprotocoltransferfileto/fromremotehostclient/servermodelclient:sidethatinitiatestransfer(eitherto/fromremote)server:remotehostftp:RFC959ftpserver:port21filetransferFTPserverFTPuserinterfaceFTPclientlocalfilesystemremotefilesystemuserathost562:ApplicationLayerFTP:thefiletransferprotocoFTP:separatecontrol,dataconnectionsFTPclientcontactsFTPserveratport21,TCPistransportprotocolclientauthorizedovercontrolconnectionclientbrowsesremotedirectorybysendingcommandsovercontrolconnection.whenserverreceivesfiletransfercommand,serveropens2nd

TCPconnection(forfile)toclientaftertransferringonefile,serverclosesdataconnection.FTPclientFTPserverTCPcontrolconnectionport21TCPdataconnectionport20serveropensanotherTCPdataconnectiontotransferanotherfile.controlconnection:“outofband”FTPservermaintains“state”:currentdirectory,earlierauthentication572:ApplicationLayerFTP:separatecontrol,dataco9.1.4文件傳輸服務(wù)——ftp[01]ftp[02]connectedto[03]220nicFTPserver(Sunos4.1)ready.[04]Name:anonymous[05]331Guestloginok,sendidentaspassword.[06]Password:abc@[07]230Guestloginok,accessrestrictionsapply.[08]ftp>cdrfc[09]250CWDcommandsuccessful.[10]ftp>getrfc1261.txtnicinfo[11]200PORTcommandsuccessful.[12]150ASCIIdataconnectionforrfc1261.txt(7,1401)(4318bytes).[13]226ASCIITransfercomplete.local:nicinforemote:rfc1261.txt4488bytesreceivedin15seconds(0.3Kbytes/s).[14]ftp>quit[15]221Goodbye.Wanttoconnect582:ApplicationLayer9.1.4文件傳輸服務(wù)——ftp[01]ftpnic9.1.4文件傳輸服務(wù)——ftp[01]ftp[02]connectedto[03]220nicFTPserver(Sunos4.1)ready.[04]Name:anonymous[05]331Guestloginok,sendidentaspassword.[06]Password:abc@[07]230Guestloginok,accessrestrictionsapply.[08]ftp>cdrfc[09]250CWDcommandsuccessful.[10]ftp>getrfc1261.txtnicinfo[11]200PORTcommandsuccessful.[12]150ASCIIdataconnectionforrfc1261.txt(7,1401)(4318bytes).[13]226ASCIITransfercomplete.local:nicinforemote:rfc1261.txt4488bytesreceivedin15seconds(0.3Kbytes/s).[14]ftp>quit[15]221Goodbye.[02]connectsuccessful

592:ApplicationLayer9.1.4文件傳輸服務(wù)——ftp[01]ftpnic9.1.4文件傳輸服務(wù)——ftp[01]ftp[02]connectedto[03]220nicFTPserver(Sunos4.1)ready.[04]Name:anonymous[05]331Guestloginok,sendidentaspassword.[06]Password:abc@[07]230Guestloginok,accessrestrictionsapply.[08]ftp>cdrfc[09]250CWDcommandsuccessful.[10]ftp>getrfc1261.txtnicinfo[11]200PORTcommandsuccessful.[12]150ASCIIdataconnectionforrfc1261.txt(7,1401)(4318bytes).[13]226ASCIITransfercomplete.local:nicinforemote:rfc1261.txt4488bytesreceivedin15seconds(0.3Kbytes/s).[14]ftp>quit[15]221Goodbye.[03]220meansserviceisready.602:ApplicationLayer9.1.4文件傳輸服務(wù)——ftp[01]ftpnic9.1.4文件傳輸服務(wù)——ftp[01]ftp[02]connectedto[03]220nicFTPserver(Sunos4.1)ready.[04]Name:anonymous[05]331Guestloginok,sendidentaspassword.[06]Password:abc@[07]230Guestloginok,accessrestrictionsapply.[08]ftp>cdrfc[09]250CWDcommandsuccessful.[10]ftp>getrfc1261.txtnicinfo[11]200PORTcommandsuccessful.[12]150ASCIIdataconnectionforrfc1261.txt(7,1401)(4318bytes).[13]226ASCIITransfercomplete.local:nicinforemote:rfc1261.txt4488bytesreceivedin15seconds(0.3Kbytes/s).[14]ftp>quit[15]221Goodbye.[04]name

612:ApplicationLayer9.1.4文件傳輸服務(wù)——ftp[01]ftpnic9.1.4文件傳輸服務(wù)——ftpFtp的屏幕信息舉例(5)[01]ftp[02]connectedto[03]220nicFTPserver(Sunos4.1)ready.[04]Name:anonymous[05]331Guestloginok,sendidentaspassword.[06]Password:abc@[07]230Guestloginok,accessrestrictionsapply.[08]ftp>cdrfc[09]250CWDcommandsuccessful.[10]ftp>getrfc1261.txtnicinfo[11]200PORTcommandsuccessful.[12]150ASCIIdataconnectionforrfc1261.txt(7,1401)(4318bytes).[13]226ASCIITransfercomplete.local:nicinforemote:rfc1261.txt4488bytesreceivedin15seconds(0.3Kbytes/s).[14]ftp>quit[15]221Goodbye.[05]331meansnameisrightandpasswordisneeded令622:ApplicationLayer9.1.4文件傳輸服務(wù)——ftpFtp的屏幕信息舉例(59.1.4文件傳輸服務(wù)——ftp[01]ftp[02]connectedto[03]220nicFTPserver(Sunos4.1)ready.[04]Name:anonymous[05]331Guestloginok,sendidentaspassword.[06]Password:abc@[07]230Guestloginok,accessrestrictionsapply.[08]ftp>cdrfc[09]250CWDcommandsuccessful.[10]ftp>getrfc1261.txtnicinfo[11]200PORTcommandsuccessful.[12]150ASCIIdataconnectionforrfc1261.txt(7,1401)(4318bytes).[13]226ASCIITransfercomplete.local:nicinforemote:rfc1261.txt4488bytesreceivedin15seconds(0.3Kbytes/s).[14]ftp>quit[15]221Goodbye.[06]632:ApplicationLayer9.1.4文件傳輸服務(wù)——ftp[01]ftpnic9.1.4文件傳輸服務(wù)——ftp[01]ftp[02]connectedto[03]220nicFTPserver(Sunos4.1)ready.[04]Name:anonymous[05]331Guestloginok,sendidentaspassword.[06]Password:abc@[07]230Guestloginok,accessrestrictionsapply.[08]ftp>cdrfc[09]250CWDcommandsuccessful.[10]ftp>getrfc1261.txtnicinfo[11]200PORTcommandsuccessful.[12]150ASCIIdataconnectionforrfc1261.txt(7,1401)(4318bytes).[13]226ASCIITransfercomplete.local:nicinforemote:rfc1261.txt4488bytesreceivedin15seconds(0.3Kbytes/s).[14]ftp>quit[15]221Goodbye.[07]

230meansregistrationisover.642:ApplicationLayer9.1.4文件傳輸服務(wù)——ftp[01]ftpnic9.1.4文件傳輸服務(wù)——ftp[01]ftp[02]connectedto[03]