2. 第二章课后习题及答案

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1、第二章1.(Q2)Foracommunicationsessionbetweenapairofprocesses,whichprocessistheclientandwhichistheserver?Answer:Theprocesswhichinitiatesthecommunicationistheclient;theprocessthatwaitstobecontactedistheserver..2.(Q3)Whatisthedifferencebetweennetworkarchitectureandapplicationarc

2、hitecture?Answer:Networkarchitecturereferstotheorganizationofthecommunicationprocessintolayers(e.g.,thefive-layerInternetarchitecture).Applicationarchitecture,ontheotherhand,isdesignedbyanapplicationdeveloperanddictatesthebroadstructureoftheapplication(e.g.,client-servero

3、rP2P)3.(Q4)Whatinformationisusedbyaprocessrunningononehosttoidentifyaprocessrunningonanotherhost?Answer:TheIPaddressofthedestinationhostandtheportnumberofthedestinationsocket.4.(Q6)ReferringtoFigure2.4,weseethatnoneoftheapplicationlistedinFigure2.4requiresbothnodatalossan

4、dtiming.Canyouconceiveofanapplicationthatrequiresnodatalossandthatisalsohighlytime-sensitive?Answer:Therearenogoodexampleofanapplicationthatrequiresnodatalossandtiming.Ifyouknowofone,sendane-mailtotheauthors5.(Q9)WhydoHTTP,FTP,SMTP,andPOP3runontopofTCPratherthanonUDP?Answ

5、er:Theapplicationsassociatedwiththoseprotocolsrequirethatallapplicationdatabereceivedinthecorrectorderandwithoutgaps.TCPprovidesthisservicewhereasUDPdoesnot.6.(Q11)Whatismeantbyahandshakingprotocol?Answer:Aprotocoluseshandshakingifthetwocommunicatingentitiesfirstexchangec

6、ontrolpacketsbeforesendingdatatoeachother.SMTPuseshandshakingattheapplicationlayerwhereasHTTPdoesnot.7.(Q13)TelnetintoaWebserverandsendamultilinerequestmessage.IncludeintherequestmessagetheIf-modified-since:headerlinetoforcearesponsemessagewiththe304NotModifiedstatuscode.

7、Answer:Issuedthefollowingcommand(inWindowscommandprompt)followedbytheHTTPGETmessagetothe“utopia.poly.edu”webserver:>telnetutopia.poly.edu80Sincetheindex.htmlpageinthiswebserverwasnotmodifiedsinceFri,18May200709:23:34GMT,thefollowingoutputwasdisplayedwhentheabovecommandswe

8、reissuedonSat,19May2007.Notethatthefirst4linesaretheGETmessageandheaderlinesinputbytheuserandthe