计算机专业英语的课文与翻译

Unit8ComputerNetworkingText1DataCommunicationsTheendequipmentcanbecomputers,printers,keyboards,CRTs,andsoon.Theyareeithergeneratesthedigitalinformationfortransmissionorusesthereceiveddigitaldata.Thisequipmentgenerallyoperatesdigitalinformationinternallyinwordunits.DTEisdataterminalequipment.Astationcontroller(STACO)isthecorrespondingunitatthesecondaries.Atonetime,theDTEwasthelastpieceofequipmentthatbelongedtothesubscriberinadatalinksystem.BetweentheDTEs,firstisthemodem,andthenisthecommunicationsequipment.ThecommunicationequipmentisownedandmaintainedbyTelco.Datacommunicationsequipment(DCE)acceptstheserialdatastreamfromtheDTE.AndDCEconvertsittosomeformofanalogsignalsuitablefortransmissiononvoice-gradelines.Atthereceiveend,theDCEperformsthereversefunction.Itconvertsthereceivedanalogsignaltoaserialdigitaldatastream.ThesimplestformofDCEisamodem(modulator/demodulator)ordataset.Atthetransmitend,themodemcanbeconsideredaformofdigital-to-analogconverter.Whileatthereceiveend,itcanbeconsideredaformofanalog-to-digitalconverter.参考译文数据通信终端设备可以是计算机、打印机、键盘、CRT等。它们可以生成要发送的数字信息，也可以使用所接收的数字数据。这种设备通常在内部以字为单位处理数字信息。DTE一般称为数据终端设备。辅助设备一方的相应设备是工作站控制器（STACO）。同时，DTE也是数据链路系统中属于用户端的最后一个设备。在两个DTE之间，先是调制解调器，接着是属于Telco电话公司维护的通信设备。数据通信设备（DCE）从DTE接收串行数据流，并将其转换成适合于在语音线路上发送的某种模拟信号形式。在接收端，DCE完成相反的功能，把接收到的模拟信号转换成串行数字数据流。最简单的DCE是调制解调器或数据传送机。在发送端，调制解调器可以视为一种数/模转换器，而在接收端则可视为一种模／数转换器。Text2ArchitectureofComputerNetworksComputernetworkisacomplexunit,itconsistsoftwoormoreconnectedcomputingunits.Itisusedforthepurposeofdatacommunicationandresourcesharing.Designofanetworkanditslogicalstructureshouldcomplywithasetofdesignprinciples.Theyinclude:theorganizationoffunctions,thedescriptionofdataformatsandprocedure.Inthefollowingtwosectionswewilldiscusstwoimportantnetworkarchitectures,theOSIreferencemodelandtheTCP/IPreferencemodel.(1)theOSIreferencemodelTheOSI(opensystemsinterconnection)modelwascreatedbytheISO.Thismodelisafoundationforcomparingprotocols;However,moreprotocolsdeviatefromtherulessetupbytheOSImodel.TheOSImodelhassevenlayers.NotethattheOSImodelitselfisnotanetworkarchitecture.Itjusttellswhateachlayershoulddo.However,ISOhasalsoproducedstandardsforallthelayers.Eachonehasbeenpublishedasaseparateinternationalstandard.(2)theTCP/IPreferencemodelTCP/IPisacommunicationprotocol;itprovidesmanydifferentnetworkingservices.TheTCP/IPInternetprotocolsuiteisformedfromtwostandards:theTCP(TransmissionControlProtocol)andtheIP(InternetProtocol).TCPmeansitisonthetransportlayer.IPmeansitisonthenetworklayer.Ontopofthetransportlayeristheapplicationlayer.Itcontainsallthehigher-levelprotocols.Theearlyonesincludedvirtualterminal(TELNET),filetransfer(FTP),electronicmail(SMTP)anddomainnameservice(DNS).Asweknow,TCP/IPisthefoundationoftheInternet.Theseprotocolsarecontinuallychangingandevolvingtosupporttheneedsoftheusercommunity.参考译文计算机网络结构计算机网络是由两个或多个计算机设备互连而成的一种复合系统，它用于数据通信和资源共享。网络设计及其逻辑结构应该遵循一套设计原则，其中包括：功能的组织以及数据格式和过程的说明。在下面的两小节里，我们将讨论两个重要的网络体系结构，即OSI参考模型和TCP/IP参考模型。(1)OSI参考模型OSI模型（开放系统互联参考模型）是由国际标准化组织（ISO）开发的一个建议。相对于其他协议来说，此种模式为基础模式。然而，更多的协议是背离OSI模型的。OSI模型有7层。应该注意的是，OSI模型本身并不是一种网络体系结构，它只是说明每一层应该做什么。然而，ISO还是对各层制定了标准，每一层都是作为一个单独的国际标准来颁布的。(2)TCP/IP参考模型TCP/IP参考模型是一种传输协议，提供了许多不同的网络服务。TCP/IP协议组由TCP（传输控制协议）和IP（网际协议）两部分组成。TCP表明是处于传输层，IP意为是在网络层。在传输层上面是应用层。应用层包括所有高层协议。早期的协议包括虚拟终端TELNET、文件传送协议FTP、电子邮件SMTP和域名服务DNS。现在我们知道，TCP/IP协议是因特网的基础。这些协议在用户们的支持下不断地改变和进化着。Text3LocalAreaNetworkALAN(Localareadatanetwork)isagroupofcomputers.Theworkdevicesconnectedtogetherusuallywithinthesamebuilding.Bydefinition,theconnectionsmustbehigh-speedandrelativelyinexpensive(e.g.tokenringorEthernet).Forexample,aLANmaybeusedtointerconnectworkstationsdistributedaroundofficeswithinasinglebuildingoragroupofbuildingssuchasauniversitycampus.LANsconsistofcarefullyselectedgroupsofcomponents(hardwareandsoftware).Theyareconfiguredforthespecificrequirementsoftheorganization.ALANisgenerallylimitedtothesizeofadepartmentoranorganization.AndaLANoftenconsistsof2to100devices.LANsusuallycontainresourcessuchasservers,printers,andconnectionstoothernetworksthroughinternetworkingdevices.Theinternetworkingdevicesincludeswitchesandrouters.InthenextsectionwewilldiscussthestructureofthedifferenttypesofLAN.(1)TopologyMostwideareanetworks,suchasthePSTN,useamesh(sometimesreferredtoasanetwork)topology.WithLANs,however,thelimitedphysicalseparationofthesubscriberDTEsallowssimplertopologiestobeused.Thefourtopologiesincommonusearestar,bus,ringandhub.ThemostwidespreadtopologyforLANsdesignedtofunctionasdatacommunicationsubnetworksfortheinterconnectionoflocalcomputer-basedequipmentisthehubtopology.Itisavariationofthebusandring.(2)TransmissionmediaTwistedpair,coaxialcableandopticalfibrearethethreemaintypesoftransmissionmediumusedforLANs.(3)MediumaccesscontrolmethodsTwotechniqueshavebeenadoptedforuseofthemediumaccesscontrolintheLANs.Oneiscarrier-sense-multiple-accesswithcollisiondetection,andtheotheriscontroltoken.参考译文局域网局域数据网(局域网)由若干计算机组成。通常是一幢楼内的工作设备被连接在一起。通过定义可知，这种连接一定是高速并且相对廉价的（如：令牌网和以太网）。例如，一个局域网可以把一幢楼里或像大学校园内楼群里的各个办公室的工作站连在一起。局域网是由精心挑选的各组设备（硬件和软件）