计算机网络英文提供给学生部分习题答案.docx
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计算机网络英文提供给学生部分习题答案.docx
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计算机网络英文提供给学生部分习题答案
SolutionofSelectedExercisesfromtheEndofChapterExercises
Chapter1-IntroductionAndOverview
1.4Towhataspectsofnetworkingdoesdatacommunicationsrefer?
Answer:
Datacommunicationsreferstothestudyoflow-levelmechanismsandtechnologiesusedtosendinformationacrossaphysicalcommunicationmedium,suchasawire,radiowave,orlightbeam.b5E2RGbCAP
1.5Whatispacket-switching,andwhyispacketswitchingrelevanttotheInternet?
Answer:
Packetswitchingdividesdataintosmallblocks,calledpackets,andincludesanidentificationoftheintendedrecipientineachpacket.Packetswitchingchangednetworkinginafundamentalway,andprovidedthebasisforthemodernInternet.Packetswitchingallowsmultiplesenderstotransmitdataoverasharednetwork.p1EanqFDPw
1.8Whatisacommunicationprotocol?
Conceptually,whattwoaspectsofcommunicationdoesaprotocolspecify?
Answer:
Acommunicationprotocolrefertoaspecificationfornetworkcommunication.Majoraspectsofaprotocolaresyntax(format>andsemantics(meaning>oftheprotocol.DXDiTa9E3d
1.9Whatisaprotocolsuite,andwhatistheadvantageofasuite?
Answer:
protocolsaredesignedincomplete,cooperativesetscalledsuitesorfamilies,insteadofcreatingeachprotocolinisolation.Eachprotocolinasuitehandlesoneaspectofcommunication。
together,theprotocolsinasuitecoverallaspectsofcommunication.Theentiresuiteisdesignedtoallowtheprotocolstoworktogetherefficiently.RTCrpUDGiT
1.11ListthelayersintheTCP/IPmodel,andgiveabriefexplanationofeach.
(SeeTextbook>1.14GiveabriefexplainofthelayersintheISOOpenSystemInterconnectionmodel.
(SeeTextbook>Chapter3-InternetApplicationsAndNetworkProgramming5PCzVD7HxA
3.1WhatarethetwobasiccommunicationparadigmsusedintheInternet?
Answer:
Therearevariousapproaches,butaccordingtotextbook,wecanspecifythemasStreamParadigmandMessageParadigm.jLBHrnAILg
3.2GivesixcharacteristicsofInternetstreamcommunication.
(SeeTextbook>xHAQX74J0X
3.3GivesixcharacteristicsofInternetmessagecommunication.
(SeeTextbook>LDAYtRyKfE
3.4Ifasenderusesthestreamparadigmandalwayssends1024bytesatatime,whatsizeblockscantheInternetdelivertoareceiver?
Answer:
streamparadigmdoesnotprovideanyguaranteesforblocksizes,soalldependsonindividualtransfer.Zzz6ZB2Ltk
3.6WhatarethethreesurprisingaspectsoftheInternet’smessagedeliverysemantics?
Answer:
TheInternet’smessagedeliveryhasthefollowingundesirablecharacteristics:
*Messagescanbelost
*Messagescanbeduplicated
*Messagescanbedeliveredout-of-orderdvzfvkwMI1
3.8WhentwoapplicationscommunicateovertheInternet,whichoneistheserver?
Answer:
Theapplicationthatwaitsforsomeotherapplicationstocontactiscalledserver,andtheapplicationthatcontactotheroneiscalledclient.rqyn14ZNXI
3.14Whattwoidentifiersareusedtospecifyaparticularserver?
Answer:
Aparticularserverisidentifiedbythefollowingidentifiers:
*Anidentifierforthecomputeronwhichaserverruns(IPAddress>
*Anidentifierforaparticularserviceonthecomputer(PortNumber>
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Chapter4-TraditionalInternetApplications
4.1Whatdetailsdoesanapplicationprotocolspecify?
(SeeTextbook>SixE2yXPq5
4.3Whatarethetwokeyaspectsofapplicationprotocols,andwhatdoeseachinclude?
(SeeTextbook>6ewMyirQFL
4.6WhatarethefourpartsofaURL,andwhatpunctuationisusedtoseparatetheparts?
Answer:
TheURLintofourcomponents:
aprotocol,acomputername,adocumentname,andparameters.Thecomputernameandprotocolportareusedtoformaconnectiontotheserveronwhichthepageresides.Andthedocumentnameandparametersareusedtorequestaspecificpage.kavU42VRUs
4.7WhatarethefourHTTPrequesttypes,andwheniseachused?
(SeeTextbook>y6v3ALoS89
4.12WhenauserrequestsanFTPdirectorylisting,howmanyTCPconnectionsareformed?
Explain.
Answer:
FTPusestwotypesofconnectionstoperformitsfunctionality,namely
*Acontrolconnectionisreservedforcommands.Eachtimetheserverneedstodownloadoruploadafile,theserveropensanewconnection.
*Adataconnectionisusedtotransferfiles.M2ub6vSTnP
4.16Listthethreetypesofprotocolsusedwithemail,anddescribeeach.
(SeeTextbook>0YujCfmUCw
4.17WhatarethecharacteristicsofSMTP?
(SeeTextbook>eUts8ZQVRd
4.20Whatarethetwomainemailaccessprotocols?
Answer:
Twomajoremailaccessprotocolsare:
*PostOfficeProtocol(POP>
*InternetMailAccessProtocol(IMAP>
Chapter6-InformationSourcesandSignalssQsAEJkW5T
6.4Stateanddescribethefourfundamentalcharacteristicsofasinewave.
(SeeTextbook>GMsIasNXkA
6.9Whatistheanalogbandwidthofasignal?
Answer:
Analogbandwidthofsignalcanbedefinedastobethedifferencebetweenthehighestandlowestfrequenciesoftheconstituentparts(i.e.,thehighestandlowestfrequenciesobtainedbyFourieranalysis>TIrRGchYzg
6.11Supposeanengineerincreasesthenumberofpossiblesignallevelsfromtwotofour.Howmanymorebitscanbesentinthesameamountoftime?
Explain.
Answer:
Thenumberoflevelsthatcanberepresentedbynbitsisgivenby2n.Soifnumberoflevelschangesfrom2→4,itmeansnumberofbitsgoesfrom1→27EqZcWLZNX
612.Whatisthedefinitionofbaud?
Answer:
Baudisdefinedasthenumberoftimesthatasignalcanchangepersecond.lzq7IGf02E
6.14Whatisthebandwidthofadigitalsignal?
Explain.
Answer:
Accordingtothedefinitionofanalogbandwidth,adigitalsignalhasinfinitebandwidthbecauseFourieranalysisofadigitalsignalproducesaninfinitesetofsinewaveswithfrequenciesthatgrowtoinfinity.zvpgeqJ1hk
6.18WhatisthechiefadvantageofaDifferentialManchesterEncoding?
Answer:
Themostimportantpropertyofdifferentialencodingisthattheencodingworkscorrectlyevenifthetwowirescarryingthesignalareaccidentallyreversed.NrpoJac3v1
6.20Ifthemaximumfrequencyaudibletoahumanearis20,000Hz,atwhatratemusttheanalogsignalfromamicrophonebesampledwhenconvertingittodigital?
Answer:
Thesamplingrate=2×fmax,sothesignalshouldbesampledat2x20,000=40,000Hz1nowfTG4KI
Chapter7-TransmissionMedia
7.2Whatarethethreeenergytypesusedwhenclassifyingphysicalmediaaccordingtoenergyused?
Answer:
Threetypesofenergyusedwhenclassifyingphysicalmediaareelectrical,electromechanical(radio>,andlightfjnFLDa5Zo
7.4Whatthreetypesofwiringareusedtoreduceinterferenceformnoise?
(SeeTextbook>tfnNhnE6e5
7.10Listthethreeformsofopticalfiber,andgivethegeneralpropertiesofeach.
(SeeTextbook>HbmVN777sL
7.21Whatistherelationshipbetweenbandwidth,signallevels,anddatarate?
Answer:
IfatransmissionsystemusesKpossiblesignallevelsandhasananalogbandwidthB,Nyquist’sTheoremstatesthatthemaximumdatarateinbitspersecond,D,is:
D=2Blog2KV7l4jRB8Hs
7.22Iftwosignallevelsareused,whatisthedataratethatcanbesentoveracoaxialcablethathasananalogbandwidthof6.2MHz?
Answer:
UsingtheD=2Blog2Krelationship,D=2*6.2*log22=2*6.2*1=12.4Mbps83lcPA59W9
7.24Ifasystemhasaninputpowerlevelof9000,andanoutputpowerlevelof3000,whatisthedifferencewhenexpressedindB?
Answer:
Decibelisexpressedas10log10(Pout/Pin>→10log10(3,000/9,000>=tobedeterminedbyreadermZkklkzaaP
7.23Ifasystemhasanaveragepowerlevelof100,anaveragenoiselevelof33.33,andabandwidthof100MHz,whatistheeffectivelimitonchannelcapacity?
Answer:
Shannontheoremspecifythemaximumdataratethatcouldbeachievedoveratransmissionsystemthatexperiencesnoise:
C=Blog2(1+S/N>=100,000,000*log2(1+100/33.33>=100,000,000*log24=200,000,000=200MbpsAVktR43bpw
7.25Ifatelephonesystemcanbecreatedwithasignal-to-noiseratioof40dBandananalogbandwidthof3000Hz,howmanybitspersecondcouldbetransmitted?
Answer:
Firstweshouldconvert40dBtoarealnumber,namelyif40=10log10S/N→S/N=10,000,UsingtheShannon’scapacityexpressionC=Blog2(1+S/N>→C=3,000log2(1+10,000>=tobedeterminedbyreader
Ch8-ReliabilityAndChannelCodingORjBnOwcEd
8.1Listandexplainthethreemainsourcesoftransmissionerrors.
(SeeTextbook>2MiJTy0dTT
8.3Inabursterror,howisburstlengthmeasured?
Answer:
Forabursterror,theburstsize,orlength,isdefinedasthenumberofbitsfromthestartofthecorruptiontotheendofthecorruption.gIiSpiue7A
8.4Whatisacodeword?
Answer:
Wecandefinethesetofallpossiblemessagestobeasetofdatawords,anddefinethesetofallpossibleencodedversionstobeasetofcodewords.Soeachpossiblecodesequenceisconsideredtobeacodeword.uEh0U1Yfmh
8.8ComputetheHammingdistanceforthefollowingpairs:
(0000,0001>,(0101,0001>,(1111,1001>,and(0001,1110>.IAg9qLsgBX
(SeeTextbook>
8.11GenerateaRACparitymatrixfora(20,12>codingofthedataword100011011111.
(SeeTextbook>WwghWvVhPE
8.15Expressthetwovaluesinthepreviousexerciseaspolynomials.Answer:
X10+X7+X5+X3+X
X4+X2+1
Ch9-TransmissionModesasfpsfpi4k
9.1Describethedifferencebetweenserialandparalleltransmission.
Answer:
Transmissionmodescanbedividedintotwofundamentalcategories:
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*Serial:
onebitissentatatime
*Parallel:
multiplebitsaresentatthesametimeBkeGuInkxI
9.2Whataretheadvantagesofparalleltransmission?
Whatisthechiefdisadvantage?
Answer:
Aparallelmodeoftransmissionhastwochiefadvantages:
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