计算机网络习题答案二英文.docx
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计算机网络习题答案二英文.docx
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计算机网络习题答案二英文
Chapter5:
DataCoding
FillIntheBlank
5-1.Itismucheasierforamachinetoprocessacodeifallthecharactersinthecodehave_____.
5-2.Thenumberofpossiblecombinationsorcharactersinacodingsystemarecalled_____.
5-3.Theminimumnumberofbitsthatwouldberequiredtoencodeonlythe26charactersofthealphabetis_____.
5-4.Thethreedifferentgroupsofcharacterassignmentsthatarenormallymadeinacodingsystemare_____,_____,and_____.
5-5.Thecodingsystemthathasenoughbitcombinationstoencodeallofthecharactersinalloftheworldslanguagesiscalled_____.
5-6.Threemajortypesofdatacompressionarecalled_____,_____,and_____.
5-7.Arguably,themostimportantdatacodingschemebecauseitisthemostlywidelyusedis_____.
5-8.Inanevenparitysystem,a1bitisaddedtoacharacter’scodewhennecessarytomakethetotalnumberof1bitsrepresentingthecharacteran_____number.
5-9.Charactercompressionisalsoknownas_____.
5-10.Characterstrippingremovestheleadingandtrailing_____charactersfromamessageandaddsthembackatthereceivingend.
5-11.Runlengthencodingreplaces_____charactersorrepetitivegroupsofcharacterswithadifferent,muchshortergroupofcharacters.
5-12.Ameasureofhowfewbitsarerequiredtoaccuratelyconveythemeaningofacharacteriscalled__________.
5-13.Bitsthatareusedtodeterminethecodepointsinacodearecalled__________.
5-14.The_____codeisan8-bitcodethathas256codepoints.
TrueorFalse
5-1.Thetermbinarydigitisabbreviatedbit.
5-2.MachinescannotsendMorsecodebecausethecodedcharactershavedifferentnumbersofcodeelements.
5-3.Itismoredifficultforamachinetoprocessacodeifallofthebitsareofthesameduration.
5-4.Whenevenparityisused,a0bitisadded,ifnecessary,tomakethetotalnumberof0bitsinthecharacteranevennumber.
5-5.TheescapecharacterinacodingsystemisadifferentcharacterthantheonethatisgeneratedwhenyoupresstheESCkeyonthekeyboardofaPC.
5-6.ASCIIisa7-bitcode.
5-7.Unicodeprovidesenoughcodepointssothatallcharactersinalllanguagesoftheworldhaveaunique16-bitcodepoint.
5-8.Codeefficiencyisameasureofhowmanyextrabitsareusedbeyondthoserequiredtoconveythemeaningofacharacter.
5-9.Datacompressionistheprocessofreducingthenumberofbitsusedtorepresentacharacter,orreducingthenumberofcharactersbeforetheyaretransmitted.
5-10.Characterstrippingistheprocessofremovingcontrolcharactersfromamessagebeforeitistransmitted.
5-11.Thebinarydigitsare1and2.
5-12.Acodeisapredeterminedsetofsymbolsthathavevariablemeanings.
5-13.Morsecodeisnotconsideredabinarycode,becauseitstwoelementsareofdifferentlength.
5-14.Abinarycodeworkswellformachinescommunicatingbyelectricalmeansbecausethe1bitsand2bitscanberepresentedbyacurrentflowthatiseitheronoroff.
5-15.Fortransmissionefficiency,itisidealtohaveacodingsystemthatusesaminimumnumberofbitstorepresenteachcharacter.
5-16.Mostcodingsystemsincludeatechniquecalledanescapecharacter.
5-17.Thenecessitytosupportescapecharacterscomplicatesthedesignofequipmentthatistocodeanddecodethedata.
5-18.TheASCIIcodeisthemostwidelyusedcodeincomputersandcommunicationsnetworkstoday.
5-19.Unicodeisa16-bitcharactercode.
MultipleChoice
5-1.Charactersthatcontrolthepositioningofinformationonaworkstationscreenorpaperarecalled_____.
a.pagecontrolcharacters
b.formateffectorcharacters
c.devicecontrolcharacters
d.screencontrolcharacters
e.aandb
5-2.Itismucheasierforamachinetoprocessacodeifthecodehasthefollowingattributes:
_____.
a.itisatruebinarycode
b.allofthecharactershavethesamenumberofbits
c.allofthebitsareperfectlyformed
d.allofthebitsarethesameduration
e.aandc
f.Alloftheabove.
5-3.Theuniquesequenceofbitsassignedtorepresentthevariouscharactersofacodearecalled_____.
a.codepoints
b.characterassignments
c.controlcharacters
d.characteralgorithms
e.Noneoftheabove.
5-4.Thepurposeofescapecharactersisto_____.
a.allowaprogramtoabortamessageprematurely
b.implementaprioritysystembyallowingonemessagetobeprematurelyendedsoanothercanbesentonthecircuit
c.actasanalternateescapecontrolcharacterwhenmorethan8bitsareneeded
d.indicatethatthecharactersthatfollowaretobeinterpretedashavinganalternatemeaning
e.indicatethataPDUhasbeenreceivedcorrectly
5-5.TheASCIIcodeisalsoknownasthe_____.
a.InternationalTelegraphAlphabet5
b.extendedASCIIcode
c.8-bitcode
d.PCcode
e.EBCDICcode
5-6.TheEBCDICcode_____.
a.wasdevelopedbyIBM
b.isan8-bitcode
c.has256codepoints
d.isusedonolderIBMmainframecomputers
e.Alloftheabove.
f.Noneoftheabove.
5-7.Unicode_____.
a.isa16-bitcode
b.wasdevelopedbyagroupofcompanies
c.supportsthecharactersofalllanguages
d.Alloftheabove.
e.Noneoftheabove.
5-8.Codeefficiencyiscalculated_____.
a.byminimizingthenumberofbitstransmittedforagivenmessage
b.bydividingtheinformationbitsbythetotalnumberofbitsinacharacter
c.bydividingthetotalnumberofbitsbytheinformationbitsinacharacter
d.bymeasuringtheerrorrateatthereceivingendofatransmission
5-9.Threemajortypesofdatacompressionare_____.
a.characterremoval,runlengthencoding,andbitcompression
b.bitstripping,doubleclocking,andcharacterstripping
c.charactercompression,Huffmancoding,andcharacterstripping
d.characterstripping,runlengthencoding,andcharactercompression
e.overclocking,transmissiondigitizing,anddoubleACKing
5-10.A10-bitcodecouldrepresenthowmanycharacters?
a.100
b.210-1
c.29
d.512
e.210
5-11.Thenumberofpossiblecombinationsorcharactersinacodingsystemiscalledthe_____.
a.characterassignment
b.codepoints
c.controlcharacter
d.codelimit
e.binarycode
5-12.Manycodingsystemsincludeanextrabit,calleda_____,forcheckingpurposes.
a.paritybit
b.paddingbit
c.controlbit
d.binarydigit
e.checkingbit
5-13.WhenanESCcharacterissentasapartofthedata,itmeansthat_____.
a.thetransmissionisbeingaborted
b.thisistheendofthetransmission
c.thecharactersthatfollowaretobeinterpretedashavinganalternatemeaning
d.thecharactersthatfollowareencrypted
e.thetransmissionshouldbeignored
5-14.Graphiccharacters_____.
a.canbedisplayedonaworkstationscreen
b.arespecialcharactersonlyusedbygraphicartists
c.areonlypresentinspecializedcodesystems
d.canalsobeusedasformateffectorcharacters
5-15Codeconversion_____.
a.changesonecharactertoanotherforsecuritypurposes
b.changesthecharactersinonecodingsystemtothoseofanothercodingsystem
c.canbereadilyperformedbyacomputer
d.Alloftheabove.
e.bandc
Chapter6:
DataCommunicationFundamentals
FILLINTHEBLANK
6-1.Thethreeattributesofasinewaveareits_____,_____,and_____.
6-2.TheFMradiobandintheUnitedStatesextendsfrom88MHzto108MHz.Itsbandwidthis_____.
6-3.Asignaldropof10dBrepresentsadropinpowerof_____times.
6-4.Aradiosignalwithafrequencyof101MHzfallswithinthe_____radioband.
6-5.Speechwithfrequenciesabove_____isattenuatedandnottransmittedthroughthepublictelephonenetwork.
6-6.Changingacommunicationsignalbyalteringitsamplitude,frequency,orphaseiscalled_____.
6-7.Theunitofsignalingrateonacommunicationcircuitiscalled_____.
6-8.Theunitofmeasureofacircuit'sdatacarryingrateiscalled_____
6-9.Sendingatribitonacircuitrequires_____(howmany)uniquesignalchangestobetransmitted?
6-10.Acircuitthatallowstransmissioninonedirectiononlyiscalleda_____circuit.
6-11.Acircuitthatallowstransmissionineitherdirectionbutnotatthesametimeiscalleda_____circuit.
6-12.Acircuitthatallowstransmissioninbothdirectionssimultaneouslyiscalleda_____circuit.
6-13.Acircuitthatallowsallofthebitsinacharactertobetransmittedsimultaneouslyiscalleda_____circuit.
6-14.Acircuitinwhichthebitsofacharacteraretransmittedoneaftertheotheronasinglecommunicationpathiscalleda_____circuit.
6-15.Themechanismbywhichcharactersynchronizationoccursinasynchronoustransmissioniscalled_____and_____bits.
6-16.Themeansbywhichthereceiverknowswhichbitstogrouptogethertoformacharacteriscalled_____.
6-17.Wheneachblockofdatatobetransmittedissurroundedwithsynchronizingandothercontrolcharactersthetransmissioniscalled_____.
6-18.Wheneachcharactertobetransmittedissurroundedwithstartandstopbits,thetransmissioniscalled_____.
6-19.The_____conditionistheidleconditiononaline.Conventionallyitisthesameasthesignalfora1bit.
6-20.Thepurposeofthe_____insynchronoustransmissionistomaintainsynchronizationbetweenthetransmittingnodeandthereceivingnode.
6-21._____modulationisbettersuitedforhigh-speedanalogtransmissionbecausethereceivermoreeasilydetectschangesin_____thanchangesinamplitudeorfrequency.
6-22._____equalizersassumethatthecircuitmeetsanaveragesetofloss,noise,anddistortionparameters,andshapethetransmittedsignalaccordingly.
6-23._____equalizersexaminetheactualparametersofthe
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