计网-第二章作业

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1、Chapter2注：括弧之中红色标注为与课本习题对应的编号2.1，2.2节后作业：1.(R2)Foracommunicationsessionbetweenapairofprocesses,whichprocessistheclientandwhichistheserver?答：Theprocessisalways-onhostcalledtheserver.Theprocesswhichinitiatesthecommunicationistheclient.2.(R3)Whatisthedifferencebetw

2、eennetworkarchitectureandapplicationarchitecture?答：Networkarchitecturereferstotheorganizationofthecommunicationprocessintolayers.Applicationarchitecture,ontheotherhand,isdesignedbyanapplicationdeveloperanddicatesthebroadstructureoftheapplication.3.(R4)Whatinform

3、ationisusedbyaprocessrunningononehosttoidentifyaprocessrunningonanotherhost?答：TheIPaddressofthedestinationhostandtheportnumberofthedestinationsocket.4.(R7)Supposeyouwantedtodoatransactionfromaremoteclienttoaserverasfastaspossible.WouldyouuseUDPorTCP?Why?答：Wewoul

4、duseUDP.WithUDP,thetransactioncanbecompletedinoneroundtriptime–theclientsendsthetransactionrequestintoaUDPsocket,andtheserversendsthereplybacktotheclient’sUDPsocket.WithTCP,aminimumoftwoRTTsareneeded–onetoset-uptheTCPconnection,andanotherfortheclienttosendthereq

5、uest,andfortheservertosendbackthereply.5.(R8)Listthefourbroadclassesofservicesthatatransportprotocolcanprovide.Foreachoftheserviceclasses,indicateifeitherUDPorTCP(orboth)providessuchaservice.答：(1)ReliableDataTransfer:TCPprovidesareliablebyte-streambetweenclienta

6、ndserverbutUDPdoesnot.(2)Throughput:Aguaranteethatacertainvalueforthroughputwillbemaintained;Neither.(3)Timing:Aguaranteethatdatawillbedeliveredwithinaspecifiedamountoftime;Neither.(4)Security:Neither.6.(R9)WhydoHTTP,FTP,SMTP,andPOP3runontopofTCPratherthanonUDP?

7、答：Theapplicationsassociatedwiththoseprotocolsrequirethatallapplicationdatabereceivedinthecorrectorderandwithoutgaps.TCPprovidesthisservicewhereasUDPdoesnot.1.(R11)Whatismeantbyahandshakingprotocol?答：Aprotocoluseshandshakingifthetwocommunicatingentitiesfirstexcha

8、ngecontrolpacketsbeforesendingdatatoeachother.SMTPuseshandshakingattheapplicationlayerwhereasHTTPdoesnot.2.3，2.4节后作业2.(R15)SupposeAlice,withaWeb-basede-mailaccount(su