局域网外文翻译一.docx
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局域网外文翻译一.docx
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局域网外文翻译一
外文翻译
论文题目
:
大型企业网络的设计与规划
姓名
:
贾龙飞
学号
:
0230
班级
:
1122102班
年级
:
2011级
专业
:
网络工程
学院
:
软件学院
指导教师
:
王志波(讲师)
完成时间
:
二〇一五年四月
NETWORKS
DATECOMMUNICATIONS
Theendequipmentwhicheithergeneratesthedigitalinformationfortransmissionorusesthereceiveddigitaldatacanbecomputer,printers,keyboards,CRTs,andsoon.Thisequipmentgenerallymanipulatesdigitalinformationinternallyinwordunits—allthebitsthatmakeupawordinaparticularpieceofequipmentaretransferredinparallel.Digitaldata,whentransmitted,areinserialform.Paralleltransmissionofan8-bitwordrequireeightpairsoftransmissionlines—notatallcost-effective.Dataterminal(DTE)isageneralphraseencompassingallofthecircuitrynecessarytoperformparallel-to-serialandserial-to-parallelconversionsfortransmissionandreceptionrespectivelyandfordatalinkmanagement.TheUART(UniversalAsynchronousReceiver/Transmitter)andUSART(UniversalAsynchronous/AsynchronousReceiver/Transmitter)arethedevicesthatperformtheparallel-to-serialandserial-to-parallelconversions.TheprimaryDTEincludesalinecontrolunit(LCUorLinCo)whichcontrolstheflowofinformationinamultipointdatalinksystem.Astationcontroller(STACO)isthecorrespondingthatbelongedtothesubscriberinadatalinksystem.BetweentheDTEs,startingwiththemodems,wascommunicationsequipmentownedandmaintainedbyTelcoproperty.
Datacommunicationsequipment(DCE)acceptstheserialdatastreamfromtheDTEandconvertsittosomeformofanalogsignalsuitablefortransmissiononvoice-gradelined.Atthereceiveend,theDCEperformsthereversefunctionofconvertingthereceivedanalogsignaltoaserialdigitaldatastream.ThesimplestformofDCEisamodem(modulator/demodulator)ordataset.Atthetransmitend,themodemcanbeconsideredaformofdigital-to-analogconverter,whileatthereceiveend,itcanconsideredaformofanalog-to-digitalconverter.Themostcommonofmodulationbymodemsarefrequencyshiftkeying(FSK),phaseshiftkeying(PSK),andquadratureamplitudemodulation(QAM).Thisisatypicallydatatransmissionmodeusingtheanalogtelephonelines.Ifyoutransmitdatabydigitalchannel(sometimesitiscalled“DigitalT-carrier”),apulseCodeModulation(PCM)equipmentmustbeused.Amicrowavetransmissionsystemcanalsobeusedforthedatacommunication.Finally,youcanusethesatellitecommunicationsystemfordatatransmission.
IfthecablesandsignallevelsusedtointerconnecttheDTEandDCEwereleftunregulated,thevariationsgeneratedwouldprobablybeproportionaltothenumberofmanufacturers.ElectronicsindustriesAssociation(EIA),anorganizationofmanufactureswithestablishingtheDTEandmodem.Thisisa25-pincablewhosepinshavedesignatedfunctionsandspecifiedsignallevels.TheRS-232Cisanticipatedtobereplacedbyanupdatestandard.
OFCOMPUTERNETWORKS
Computernetworkisacomplexconsistingoftwoormoreconnedcomputingunits,itisusedforthepurposeofdatacommunicationandresourceresourcesharing.Designofanetworkanditslogicalstructureshouldcomplywithasetofdesignprinciples,includingtheorganizationoffunctionsandthedescriptionofdataformatsandprocedure.Thisisthenetworkarchitectureandsocalledasasetoflayersandprotocols,becausethearchitectureisalayer-based.
Inthenexttwosectionswewilldiscusstwoimportantnetworkarchitectures,theOSIreferencemodelandtheTCP/IPreferencemodel.
OSIReferenceModel
TheOSImodelisshownin(minusthephysicalmedium).ThismodelisbasedonaproposaldevelopedbytheInternationalStandardsOrganizations(OSI)asthefirststeptowardinternationalstandardizationoftheprotocolsusedinthevariouslayers.ThemodeliscalledtheISOOSI(OpenSystemInterconnection)ReferenceModelbecauseitdealswithconnectingopensystems--thatis,systemsthatareopenforcommunicationwithothersystems,WewillusuallyjustcallittheOSImodelforshort.
TheOSImodelhassevenhassevenlayers.NotethattheOSImodelitselfisnotanetworkarchitecturebecauseitdoesnotspecifytheexactservicesandprotocolstobeusedineachlayer.Itjusttellswhateachlayershoulddo.However,However,ISOhasalsoproducedstandardsforallthelayers,althoughthesearenotpartofthereferencemodelitself.Eachonehasbeenpublishedasaseparateinternationalstandard.
TCP/IPReferenceModel
TheTCP/IPreferencemodelisanearlytransportprotocolwhichwasdesignedbytheUSDepartmentofDefence(DOD)aroundin1978.ItisoftenclaimedthatitgaverisetheOSI“connectionless”modeofoperation.TCP/IPisstillusedextensivelyandiscalledasaindustrialstandardofinternetworkinfact,TCP/IPhastwoparts:
TCPandIP.TCPmeansitisonthetransportlayerandIPmeansitisonthenetworklayerseparately.
aretwoend-to-endprotocolsinthetransportlayer,oneofwhichisTCP(TransmissionControlProtocol),anotherisUDP(UserDatagramProtocol).TCPisaconnection-orientedprotocolthatallowsabytestreamoriginatingononemachinetobedeliveredwithouterroronanyothermachineintheinternet.UDPisanunreliable,connectionlessprotocolforapplicationthatdonotwantTCP’ssequencingofflowscontrolflowcontrolandwishtoprovidetheirown.
networklayerdefinesanofficialpacketformatandprotocolcalledIP(Internetprotocol).ThejobofthenetworklayeristodeliverIPpacketswheretheyaresupposedtogo.
TheTCP/IPReferenceModelisshowninOntopofthetransportlayeristheapplicationlayer,Itcontainsallthehigher-levelprotocols.Theearlyonesincludedvirtualterminal(TELNET),filetransfer(FTP),electronicmail(SMTP)anddomainnameservice(DNS).
AREANETWORK
Awideareanetwork,orWAN,spansalargegeographicalarea,oftenacountryorcontinent.Itcontainsacollectionofmachinesintendedforrunninguser(i.e.,application)programs.Wewillfollowtraditionalusageandcallthesemachineshosts.Byacommunicationsubnet,orjustsubnetforshort.Thejobofthesubnetistocarrymessagesfromhosttohost,justasthetelephonesystemcarrieswordsfromspeakertolistener.Byseparatingthepurecommunicationaspectsofthenetwork(thesubnet)fromtheapplicationaspects(thehosts),thecompletenetworkdesignisgreatlysimplified.Relationbetweenhostsandthesubnetisshownin.
Oneofmanymethodsthatcanbeusedtocategorizewideareanetworksiswithrespecttotheflowofinformationonatransmissionfacility.Ifweusethismethodtocategorizewideareanetworks,wecangroupthemintothreebasictypes:
circuitswitched,leasedlineandpacketswitched.
SWITCHEDNETWORKS
Themostpopulartypeofnetworkandtheonealmostallreadersuseonadailybasisisacircuitswitchednetwork.Thepublicswitchedtelephonenetwork,however,isnotlimitedtothetelephonecompany,Bypurchasingappropriateswitchingequipment,anyorganizationcanconstructtheirowninternalcircuitswitchednetworkand,ifdesired,provideoneormoreinterfacestothepublicswitchednetworktoallowvoiceanddatatransmissiontoflowbetweenthepublicnetworkandtheirprivateinternalnetwork
2.LEASEDLINENETWORKS
Thisisadedicatednetworkconnectedbyleasedlines.Leasedlineisacommunicationslinereservedfortheexclusiveuseofaleasingcustomerwithoutinter-exchangeswitchingarrangements.Leasedorprivatelinesarededicatedtotheuser.Thisadvantageisthattheterminalorcomputerisaalwaysphysicallyconnectedtotheline.Veryshortresponsetimesaremetwithservice.
SWITCHINGNETWORKS
Apacketnetworkisconstructedthroughtheuseofequipmentthatassemblesanddisassemblespackets,equipmentthatroutespacket,andtransmissionfacilitiesusedtoroutepacketsfromtheoriginatortothedestinationdevice.Sometypesofdataterminalequipment(DTE)cancreatetheirownpackets,whileothertypesofDTErequiretheconversionoftheirprotocolintopacketsthroughtheuseofapacketassembler/disassemble(PAD).Packetsareroutedthroughthenetworkbypacketswitches.Packetswitchesexaminethedestinationofpacketsastheyflowthroughthenetworkandtransferthepacketsontotrunksinterconnectingswitchesbaseduponthepacketdestinationdestinationandnetworkactivity.
Manyolderpubicnetworksfollowastandardcalled.Itwasdevelopedduring1970sbyCCITTtoprovideaninterfacebetweenpublicpacket-switchednetworkandtheircustomers.
CCITTRecommendationcontrolstheaccessfromapacketmodeDTE,suchasaterminaldeviceorcomputersystemcapableofformingpackets,totheDCEatapacketmode.CCITTRecommendationcontrolstheinterfacebetweennon-packetmodedevicesthatcannotinterfacebetweenthePADandthehostcomputer.CCITTRecommendationspecifiestheparametersettingsonthePADandspecifiestheinterfacebetweenpacketnetwork.
AREANETWORK
Localareadatanetwork,normallyreferredtosimplyaslocalareanetworkorLANs,areusedtointerconnectdistributedcommunitiesofcomputer-basedDTEslocatedwithinabuildingorlocalizedgroupofbuilding.Forexample,aLANmaybeusedtointerconnectworkstationsdistributedaroundofficeswithinasinglebuildingoragroupofbuildingssuchasauniversitycampus.Alternatively,itmaybecomplex.Sincealltheequipmentislocatedwithinasingleestablishment,however,LANsarenormallyinstalledandmaintainedbytheorganization.Hencetheyarealsoreferredtoasprivatedatanetworks.
ThemaindifferencebetweenacommunicationpathestablishedusingaLANandaconnectionmadethroughapublicdatanetworkisthataLANnormally
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