计算机网络英文版——提供给学生部分习题答案.doc

计算机网络英文版——提供给学生部分习题答案.doc

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SolutionofSelectedExercisesfromtheEndofChapterExercises

Chapter1-IntroductionAndOverview

1.4Towhataspectsofnetworkingdoesdatacommunicationsrefer?

Answer:

Datacommunicationsreferstothestudyoflow-levelmechanismsandtechnologiesusedtosendinformationacrossaphysicalcommunicationmedium,suchasawire,radiowave,orlightbeam.

1.5Whatispacket-switching,andwhyispacketswitchingrelevanttotheInternet?

Answer:

Packetswitchingdividesdataintosmallblocks,calledpackets,andincludesanidentificationoftheintendedrecipientineachpacket.Packetswitchingchangednetworkinginafundamentalway,andprovidedthebasisforthemodernInternet.Packetswitchingallowsmultiplesenderstotransmitdataoverasharednetwork.

1.8Whatisacommunicationprotocol?

Conceptually,whattwoaspectsofcommunicationdoesaprotocolspecify?

Answer:

Acommunicationprotocolrefertoaspecificationfornetworkcommunication.Majoraspectsofaprotocolaresyntax（format）andsemantics（meaning）oftheprotocol.

1.9Whatisaprotocolsuite,andwhatistheadvantageofasuite?

Answer:

protocolsaredesignedincomplete,cooperativesetscalledsuitesorfamilies,insteadofcreatingeachprotocolinisolation.Eachprotocolinasuitehandlesoneaspectofcommunication;together,theprotocolsinasuitecoverallaspectsofcommunication.Theentiresuiteisdesignedtoallowtheprotocolstoworktogetherefficiently.

1.11ListthelayersintheTCP/IPmodel,andgiveabriefexplanationofeach.

（SeeTextbook）

1.14GiveabriefexplainofthelayersintheISOOpenSystemInterconnectionmodel.

（SeeTextbook）

Chapter3-InternetApplicationsAndNetworkProgramming

3.1WhatarethetwobasiccommunicationparadigmsusedintheInternet?

Answer:

Therearevariousapproaches,butaccordingtotextbook,wecanspecifythemasStreamParadigmandMessageParadigm.

3.2GivesixcharacteristicsofInternetstreamcommunication.

（SeeTextbook）

3.3GivesixcharacteristicsofInternetmessagecommunication.

（SeeTextbook）

3.4Ifasenderusesthestreamparadigmandalwayssends1024bytesatatime,whatsizeblockscantheInternetdelivertoareceiver?

Answer:

streamparadigmdoesnotprovideanyguaranteesforblocksizes,soalldependsonindividualtransfer.

3.6WhatarethethreesurprisingaspectsoftheInternet’smessagedeliverysemantics?

Answer:

TheInternet’smessagedeliveryhasthefollowingundesirablecharacteristics:

*Messagescanbelost

*Messagescanbeduplicated

*Messagescanbedeliveredout-of-order

3.8WhentwoapplicationscommunicateovertheInternet,whichoneistheserver?

Answer:

Theapplicationthatwaitsforsomeotherapplicationstocontactiscalledserver,andtheapplicationthatcontactotheroneiscalledclient.

3.14Whattwoidentifiersareusedtospecifyaparticularserver?

Answer:

Aparticularserverisidentifiedbythefollowingidentifiers:

*Anidentifierforthecomputeronwhichaserverruns（IPAddress）

*Anidentifierforaparticularserviceonthecomputer（PortNumber）

Chapter4-TraditionalInternetApplications

4.1Whatdetailsdoesanapplicationprotocolspecify?

（SeeTextbook）

4.3Whatarethetwokeyaspectsofapplicationprotocols,andwhatdoeseachinclude?

（SeeTextbook）

4.6WhatarethefourpartsofaURL,andwhatpunctuationisusedtoseparatetheparts?

Answer:

TheURLintofourcomponents:

aprotocol,acomputername,adocumentname,andparameters.Thecomputernameandprotocolportareusedtoformaconnectiontotheserveronwhichthepageresides.Andthedocumentnameandparametersareusedtorequestaspecificpage.

4.7WhatarethefourHTTPrequesttypes,andwheniseachused?

（SeeTextbook）

4.12WhenauserrequestsanFTPdirectorylisting,howmanyTCPconnectionsareformed?

Explain.

Answer:

FTPusestwotypesofconnectionstoperformitsfunctionality,namely

*Acontrolconnectionisreservedforcommands.Eachtimetheserverneedstodownloadoruploadafile,theserveropensanewconnection.

*Adataconnectionisusedtotransferfiles.

4.16Listthethreetypesofprotocolsusedwithemail,anddescribeeach.

（SeeTextbook）

4.17WhatarethecharacteristicsofSMTP?

（SeeTextbook）

4.20Whatarethetwomainemailaccessprotocols?

Answer:

Twomajoremailaccessprotocolsare:

*PostOfficeProtocol（POP）

*InternetMailAccessProtocol（IMAP）

Chapter6-InformationSourcesandSignals

6.4Stateanddescribethefourfundamentalcharacteristicsofasinewave.

（SeeTextbook）

6.9Whatistheanalogbandwidthofasignal?

Answer:

Analogbandwidthofsignalcanbedefinedastobethedifferencebetweenthehighestandlowestfrequenciesoftheconstituentparts（i.e