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ID:33613988
大小:56.99 KB
页数:7页
时间:2019-02-27
《communication networks -14 -application and presentation layers》由会员上传分享,免费在线阅读,更多相关内容在教育资源-天天文库。
1、Module4StandardsVersion1ECE,IITKharagpurLesson14Application&PresentationLayersVersion1ECE,IITKharagpurLESSONOBJECTIVEGeneralThislessonisdesignedtogivethereaderanoverviewofthestandardsfollowedinthetopmostlayersoftheOSIreferencemodelviz.ApplicationlayerandPresentationlayer.SpecificOncompletionoft
2、hislesson,thelearnershallbeableto1.UnderstandtheworkingofTelnetprotocol.2.IdentifytheapplicationsofFTP.3.OutlinetheprocedureofHTTP.4.7.1INTRODUCTIONThislessoncontinuesourexplorationofnetworkingstandardsbyexamininghighlevelinternetservicesandtheapplicationandpresentationlayerstandardsthatsupport
3、them.Theseservicesdeterminehowuserspursuetheinternet.Wewillseethatthesehighlevelservicesprovideincreasedcommunicationfunctionalityandallowusersandprogramstointeractwithautomatedservicesonremotemachinesandwithremoteusers.WeshallnowlookatTELNET,FTPandHTTPindetail.4.7.2TELNETPROTOCOLTheTCP/IPproto
4、colsuiteincludesasimpleremoteterminalprotocolcalledTELNETthatallowsuserstologintoacomputeracrosstheinternet.TELNETestablishesaTCPconnectionandthenpasseskeystrokesfromtheuser’skeyboarddirectlytotheremotecomputerasiftheyhadbeentypedonakeyboardattachedtothemachine.TELNETalsocarriesoutputfromtherem
5、otemachinebacktotheuser’sscreen.Theserviceiscalledtransparentbecauseitgivestheappearancethattheuser’skeyboardanddisplayattachdirectlytotheremotemachine.TELNETishowevernotassophisticatedassomeremoteterminalprotocols.TELNETclientsoftwareallowstheusertospecifytheremotemachineeitherbyspecifyingitsd
6、omainnameorIPaddress.TELNEToffersthreePage:Lesson14.1Version1ECE,IITKharagpurbasicservices.Firstitdefinesanetworkvirtualterminalthatprovidesastandardinterfacetoremotesystems.Clientprogramsdonothavetounderstandthedetailsofallpossibleremotesystems;theyarebuilttousethestandardinterface.SecondTELNE
7、Tincludesamechanismthatallowstheclientandservertonegotiateoptions,anditprovidesasetofstandardoptions.FinallyTELNETtreatsbothendsoftheconnectionsymmetrically.Inparticular,TELNETdoesnotforceclientinputtocomefromakeyboard,nordoesitfo
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