communication networks -14 -application and presentation layers

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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