《计算机网络与因特网》douglarsecorner著第六版英文答案Word文件下载.doc

《计算机网络与因特网》douglarsecorner著第六版英文答案Word文件下载.doc

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• Layer3:

Internet:

ProtocolsintheInternetlayerformthefundamentalbasisforthe

Internet.Layer3protocolsspecifycommunicationbetweentwocomputersacrosstheInternet

•Layer4:

Transport:

ProtocolsintheTransportlayerprovideforcommunicationfromanapplicationprogramononecomputertoanapplicationprogramonanother.

• Layer5:

Application:

ProtocolsinthetoplayeroftheTCP/IPstackspecifyhowa

pairoapplicationsinteractwhentheycommunicate.

1.4Whatisaprotocolsuite,andwhatistheadvantageofasuite?

protocolsaredesignedincomplete,cooperativesetscalledsuitesorfamilies,insteadofcreatingeachprotocolinisolation.Eachprotocolinasuitehandlesoneaspectofcommunication;

together,theprotocolsinasuitecoverallaspectsofcommunication.Theentiresuiteisdesignedtoallowtheprotocolstoworktogetherefficiently.

1.5DescribetheTCP/IPlayeringmodel,andexplainhowitwasderived.

1.6ProvidereasonsforInternetgrowthinrecentyears.

1.7Whatisinteroperability,andwhyisitespeciallyimportantintheInternet?

1.8Accordingtothetext,isitpossibletodevelopInternetapplicationswithoutunderstandingthearchitectureoftheInternetandthetechnologies?

Supportyouranswer.

©

2009PearsonEducation,Inc.,UpperSaddleRiver,NJ.Allrightsreserved.ThispublicationisprotectedbyCopyrightandwrittenpermissionshou7ldbeobtainedfrom

thepublisherpriortoanyprohibitedreproduction,storageinaretrievalsystem,ortransmissioninanyformorbyanymeans,electronic,mechanical,photocopying,recording,orlikewise.Forinformationregardingpermission（s）,writeto:

RightsandPermissionsDepartment,PearsonEducation,Inc.,UpperSaddleRiver,NJ07458.

Yes,possibletowritecodethatcommunicatesoveranetwork,withoutunderstandingthehardwareandsoftwaretechnologiesthatareusedtotransferdatafromoneapplicationtoanother.However,knowledgeoftheunderlyingnetworksystemallowsaprogrammertowritebettercode.

1.9Towhataspectsofnetworkingdoesdatacommunicationsrefer?

Datacommunicationsreferstothestudyoflow-levelmechanismsandtechnologiesusedtosendinformationacrossaphysicalcommunicationmedium,suchasawire,radiowave,orlightbeam.

1.10Whatisacommunicationprotocol?

Conceptually,whattwoaspectsofcommunicationdoesaprotocolspecify?

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

1.11Listmajorstandardizationorganizationsthatcreatestandardsfordatacommunicationsandcomputernetworking.

Variousnationalandinternationalorganizationsareinvolvedinstandardizationofcommunicationsandnetworkingservices.Tolistfew:

• InternationalOrganizationforStandardization（ISO）

• InternationalTelecommunicationsUnion,TelecommunicationStandardization

Sector（ITU-T）

• InstituteofElectricalandElectronicsEngineers（IEEE）

• InternetEngineeringTaskForce（IETF）

1.12GiveabriefexplainofthelayersintheISOOpenSystemInterconnectionmodel.

ISOOSImodelconsistsof7layers,namely:

• Layer7:

Application

• Layer6:

Presentation

Session

• Layer4:

Transport

Network

DataLink

Physical

Readerisexpectedtofindoutshortexplanationofeachlayer.

1.13Whatispacket-switching,andwhyispacketswitchingrelevanttotheInternet?

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

1.14Explainhowheadersareaddedandremovedasdatapassesthroughalayeredmodel.

eachlayeronthesendingcomputerprependsextrainformationontothepacket;

thecorrespondingprotocollayeronthereceivingcomputerremovesandusestheextrainformation.

Chapter-2InternetTrends

2.1DescribetheevolutioninaudiothathasoccurredintheInternet.

Thetrendinaudioprocessinghasbeenasfollows:

AlertSoundsÆ

HumanVoiceÆ

AudiClipsÆ

High-FidelityAudio

2.2AssumethatonehundredmillionnewcomputersareaddedtotheInterneteachyear.Ifcomputersareaddedatauniformrate,howmuchtimeelapsesbetweentwosuccessiveadditions?

2.3DescribeInternetapplicationsthatyouuseregularlythatwerenotavailabletoyourparentswhentheywereyourage.

2.4Whywassharingofcomputationalresourcesimportantinthe1960s?

2.5WhatshiftinInternetuseoccurredwhentheWorldWideWebfirstappeared?

2.6TheplotinFigure2.1showsthatInternetgrowthdidnotstartuntilafter1995.Whyisthefiguremisleading?

ResearcherscomputersworkingfortheAdvancedResearchProjectsAgency（ARPA）ofUSDepartmentofDefense（DoD）neededpowerfulandcomputerswereincrediblyexpensive.TheARPAbudgetwasinsufficienttofundmanycomputers.TheARPAplannedtointerconnectallcomputerswithadatanetworkanddevisesoftwarethatwouldallowaresearchertousewhichevercomputerwasbestsuitedtoperformagiventask.

2.7ListthestepsinthetransitioningraphicspresentationfromtheearlyInternettothecurrentInternet.

Thetrendinthegraphicpresentationhasbeenasfollows:

TextÆ

GraphicImagesÆ

VideoClipsÆ

Full-MotionVideo

2.8WhatInternettechnologyisthetelephonesystemusing?

SomecurrenttelephonesystemsusesVoice-OverIPtechnology.Readerisencouragedtorefertolaterchaptersfordetails.

2.9ExtendtheplotinFigure2.2,andestimatehowmanycomputerswillbeconnectedtotheInternetby2020.

2.10WhatimpactisInternettechnologyhavingonthecabletelevisionindustry?

2.11ListfournewInternetapplications,andtellthegroupsforwhicheachisimportant.

2.12WhyistheswitchfromwiredInternetaccesstowirelessInternetaccesssignificant?

Chapter3-InternetApplicationsAndNetworkProgramming

3.2WhatarethetwobasiccommunicationparadigmsusedintheInternet?

Therearevariousapproaches,butaccordingtotextbook,wecanspecifythemasStreamParadigmandMessageParadigm.

3.12GivesixcharacteristicsofInternetstreamcommunication.

CharacteristicsofInternetstreamcommunicationcanbelistedasfollows:

• Connection-oriented

• 1-to-1communication

• Sequenceofindividualbytes

• Arbitrarylengthtransfer

• Usedformultimediaapplications

• BuiltonUDPprotocol

3.4GivesixcharacteristicsofInternetmessagecommunication.

CharacteristicsofInternetmessagecommunicationcanbelistedasfollows:

• Connectionless

• Many-to-manycommunication

• Sequenceofindividualmessages

• Eachmessagelimitedto64Kbytes

• Usedbymostapplications

• BuiltonTCPprotocol

3.13Ifasenderusesthestreamparadigmandalwayssends1024bytesatatime,whatsizeblockscantheInternetdelivertoareceiver?

streamparadigmdoesnotprovideanyguaranteesforblocksizes,soalldependsonindividualtransfer.

3.6Ifasenderwantstohavecopiesofeachdatablockbeingsenttothreerecipients,whichparadigmshouldthesenderchoose?

Themessageparadigmissuitableforsuchtransfer,sinceitallowsmany-to-manycommunication

3.21WhatarethethreesurprisingaspectsoftheInternet’smessagedeliverysemantics?

TheInternet’smessagedeliveryhasthefollowingundesirablecharacteristics:

• Messagescanbelost

• Messagescanbeduplicated

• Messagescanbedeliveredout-of-order

3.19Givethegeneralalgorithmthataconnection-orientedsystemuses.

Theinteractionbetweentwoconnection-orientedpartiescanbesummarizedas:

• Setting-upconnectionbetweentwoparties

• Exchangeinformation

• Terminatetheconnection

3.25WhentwoapplicationscommunicateovertheInternet,whichoneistheserver?

Theapplicationthatwaitsforsomeotherapplicationstocontactiscalledserver,andtheapplicationthatcontactotheroneiscalledclient.

3.14Compareandcontrastaclientandserverapplicationbysummarizingcharacteristicsofeach.

3.5Whatisthedifferencebetweenaserverandaserver-classcomputer?

Theservertermreferstoaprogramthatwaitspassivelyforcommunication,

andnottothecomputeronwhichitexecutes.However,whenacomputerisdedicatedtorunningoneormoreserverprograms,thecomputeritselfissometimescalledaserver.HardwarevendorscontributetotheconfusionbecausetheyclassifycomputersthathavefastCPUs,largememories,andpowerfuloperatingsystemsasservermachines.

3.20Candataflowfromaclienttoaserver?

Explain.

Yes,datamayflowinbothdirections（