《计算机专业英语》-Unit7ComputerNetwork

TextA:ComputerNetwork下一页返回TextA:ComputerNetworkAcomputernetwork,oftensimplyreferredtoasanetwork,isacollectionofcomputersanddevicesconnectedbycommunicationschannelsthatfacilitatescommunicationsamongusersandallowsuserstoshareresourceswithotherusers.Networksmaybeclassifiedaccordingtoawidevarietyofcharacteristics.Thisarticleprovidesageneraloverviewoftypesandcategories.上一页下一页返回TextA:ComputerNetwork1.IntroductionAcomputernetworkallowssharingofresourcesandinformationamongdevicesconnectedtothenetwork.TheAdvancedResearchProjectsAgency(ARPA)fundedthedesignoftheAdvancedResearchProjectsAgencyNetwork(ARPANET)fortheUnitedStatesDepartmentofDefense.Itwasthefirstoperationalcomputernetworkintheworld.Developmentofthenetworkbeganin1969,basedondesignsdevelopedduringthe1960s.上一页下一页返回TextA:ComputerNetwork2.PurposeComputernetworkscanbeusedforseveralpurposes:Facilitatingcommunications.Usinganetwork,peoplecancommunicateefficientlyandeasilyviaemail,instantmessaging,chatrooms,telephony,videotelephonecalls,andvideoconferencing.Sharinghardware.Inanetworkenvironment,eachcomputeronanetworkcanaccessandusehardwareonthenetwork.Sharingfiles,data,andinformation.Inanetworkenvironment,anyauthorizedusercanaccessdataandinformationstoredonothercomputersonthenetwork.Sharingsoftware.Usersconnectedtoanetworkcanaccessapplicationprogramsonthenetwork.上一页下一页返回TextA:ComputerNetwork3.TypesofNetworksCommontypesofcomputernetworksmaybeidentifiedbytheirscale.(1)PersonalareanetworkApersonalareanetwork(PAN)isacomputernetworkusedforcommunicationamongcomputersanddifferentinformationtechnologicaldevicesclosetooneperson.SomeexamplesofdevicesthatareusedinaPANarepersonalcomputers,printers,faxmachines,telephones,PDAs,scanners,andevenvideogameconsoles.APANmayincludewiredandwirelessconnectionsbetweendevices.ThereachofaPANtypicallyextendsto10meters.AwiredPANisusuallyconstructedwithUSBandFirewireconnectionswhiletechnologiessuchasBluetoothandinfraredcommunicationtypicallyformawirelessPAN.上一页下一页返回TextA:ComputerNetwork(2)LocalareanetworkAlocalareanetwork(LAN)isanetworkthatconnectscomputersanddevicesinalimitedgeographicalareasuchashome,school,computerlaboratory,officebuilding,orcloselypositionedgroupofbuildings.Eachcomputerordeviceonthenetworkisanode.CurrentwiredLANsaremostlikelybasedonEthernettechnology,althoughnewstandardslikeITUTG.hnalsoprovideawaytocreateawiredLANusingexistinghomewires(coaxialcables,phonelinesandpowerlines).上一页下一页返回TextA:ComputerNetwork(3)HomeareanetworkAhomeareanetworkisaresidentialLANwhichisusedforcommunicationbetweendigitaldevicestypicallydeployedinthehome,usuallyasmallnumberofpersonalcomputersandaccessories,suchasprintersandmobilecomputingdevices.AnimportantfunctionisthesharingofInternetaccess,oftenabroadbandservicethroughaCATVorDigitalSubscriberLine(DSL)provider.上一页下一页返回TextA:ComputerNetwork(4)CampusnetworkAcampusnetworkisacomputernetworkmadeupofaninterconnectionoflocalareanetworks(LANs)withinalimitedgeographicalarea.Thenetworkingequipments(switches,routers)andtransmissionmedia(opticalfiber,copperplant,Cat5cabling,etc.)arealmostentirelyownedbythecampustenant/owner:anenterprise,university,government,etc.上一页下一页返回TextA:ComputerNetwork(5)WideareanetworkAwideareanetwork(WAN)isacomputernetworkthatcoversalargegeographicareasuchasacity,country,orspansevenintercontinentaldistances,usingacommunicationschannelthatcombinesmanytypesofmediasuchastelephonelines,cables,andairwaves.AWANoftenusestransmissionfacilitiesprovidedbycommoncarriers,suchastelephonecompanies.WANtechnologiesgenerallyfunctionatthelowerthreelayersoftheOSIreferencemodel:thephysicallayer,thedatalinklayer,andthenetworklayer.上一页下一页返回TextA:ComputerNetwork(6)GlobalareanetworkAglobalareanetwork(GAN)isanetworkusedforsupportingmobilecommunicationsacrossanarbitrarynumberofwirelessLANs,satellitecoverageareas,etc.Thekeychallengeinmobilecommunicationsishandingofftheusercommunicationsfromonelocalcoverageareatothenext.InIEEEProject802,thisinvolvesasuccessionofterrestrialwirelesslocalareanetworks(WLAN).上一页下一页返回TextA:ComputerNetworkWordsandExpressionsfacilitate:v.使容易;帮助;促进videoconference:n.电视电话会议PDA:PersonalDigitalAssistant,个人数据处理机console:n.柜子,放电视机或收音机的台子;控制台Bluetooth:n.蓝牙技术infrared：adj.红外线的

上一页下一页返回TextA:ComputerNetworknode:n.连接点,从不同方向接收和传送传输信号的点(因特网用语)Ethernet：n.以太网,当地网络的标准技术(计算机用语)ITUT：国际电信联盟电信标准化部分coaxialcable:同轴电缆residential:n.住宅的,与居住有关的deploy:v.使展开;使疏开;展开;部署accessory:n.附件;助理程序上一页下一页返回TextA:ComputerNetworkCATV:75欧姆的同轴电缆,有时也称作CATV电缆DSL:数字用户线路，是以电话线为传输介质的传输技术组合switch:n.开关,转换;router:n.安排路线的人或其他;引导信息跨过网上到它们正确终点的硬件装置opticalfiber:光纤Cat5cabling:5类布线上一页下一页返回TextA:ComputerNetworkNotes①TheAdvancedResearchProjectsAgency(ARPA)fundedthedesignoftheAdvancedResearchProjectsAgencyNetwork(ARPANET)fortheUnitedStatesDepartmentofDefense.

美国远景研究规划局为美国国防部的阿帕网的设计提供资助。②SomeexamplesofdevicesthatareusedinaPANarepersonalcomputers,printers,faxmachines,telephones,PDAs,scanners,andevenvideogameconsoles.

一些个人区域网中用到的设备有计算机、打印机、传真机、电话、个人数据处理机、扫描仪甚至视频游戏机等。上一页下一页返回TextA:ComputerNetwork③CurrentwiredLANsaremostlikelybasedonEthernettechnology,althoughnewstandardslikeITUTG.hnalsoprovideawaytocreateawiredLANusingexistinghomewires(coaxialcables,phonelinesandpowerlines).

目前的有线局域网大多是基于以太网技术的，尽管国际电信联盟远程通信标准化组的G.hn（标准）也提供一种利用现有的家用线路（同轴电缆、电话线和电线）组建的有线局域网。上一页下一页返回TextA:ComputerNetwork④AhomeareanetworkisaresidentialLANwhichisusedforcommunicationbetweendigitaldevicestypicallydeployedinthehome,usuallyasmallnumberofpersonalcomputersandaccessories,suchasprintersandmobilecomputingdevices.⑤Thenetworkingequipments(switches,routers)andtransmissionmedia(opticalfiber,copperplant,Cat5cabling,etc.)arealmostentirelyownedbythecampustenant/owner:anenterprise,university,government,etc.上一页返回TextB:HistoryoftheInternetTheInternetisaglobalsystemofinterconnectedcomputernetworksthatusethestandardInternetProtocolSuite(TCP/IP)toservebillionsofusersworldwide.Itisanetworkofnetworksthatconsistsofmillionsofprivate,public,academic,business,andgovernmentnetworksoflocaltoglobalscopethatarelinkedbyabroadarrayofelectronicandopticalnetworkingtechnologies.下一页返回TextB:HistoryoftheInternetMosttraditionalcommunicationsmedia,suchastelephoneandtelevisionservices,arereshapedorredefinedusingthetechnologiesoftheInternet,givingrisetoservicessuchasVoiceoverInternetProtocol(VoIP)andIPTV.NewspaperpublishinghasbeenreshapedintoWebsites,blogging,andwebfeeds.TheInternethasenabledoracceleratedthecreationofnewformsofhumaninteractionsthroughinstantmessaging,Internetforums,andsocialnetworkingsites.上一页下一页返回TextB:HistoryoftheInternetTheoriginsoftheInternetreachbacktothe1960swhentheUnitedStatesfundedresearchprojectsofitsmilitaryagenciestobuildrobust,faulttolerantanddistributedcomputernetworks.ThisresearchandaperiodofcivilianfundingofanewU.S.backbonebytheNationalScienceFoundationspawnedworldwideparticipationinthedevelopmentofnewnetworkingtechnologiesandledtothecommercializationofaninternationalnetworkinthemid1990s,andresultedinthefollowingpopularizationofcountlessapplicationsinvirtuallyeveryaspectofmodernhumanlife.Asof2009,anestimatedquarterofEarth’spopulationusestheservicesoftheInternet.上一页下一页返回TextB:HistoryoftheInternetFollowingcommercializationandintroductionofprivatelyrunInternetserviceprovidersinthe1980s,andtheInternet’sexpansionforpopularuseinthe1990s,theInternethashadadrasticimpactoncultureandcommerce.Thisincludestheriseofnearinstantcommunicationbyelectronicmail(email),textbaseddiscussionforums,andtheWorldWideWeb.InvestorspeculationinnewmarketsprovidedbytheseinnovationswouldalsoleadtotheinflationandsubsequentcollapseoftheDotcombubble.Butdespitethis,theInternetcontinuestogrow,drivenbycommerce,greateramountsofonlineinformationandknowledgeandsocialnetworkingknownasWeb2.0.上一页下一页返回TextB:HistoryoftheInternetWordsandExpressionsinterconnected:adj.互联的InternetProtocolSuite：因特网协议套件reshape：v.重塑redefine：v.重新界定VoiceoverInternetProtocol：因特网声传协议blog：n.博客robust：adj.强健的；结实的Fault-tolerant：adj.容忍错误的上一页下一页返回TextB:HistoryoftheInternetcivilian：n.平民backbone：n.骨干；中枢NationalScienceFoundation：美国国家科学基金会commercialization：n.商业化prevalent：adj.流行的mainframecomputermodel：主机模式packetswitchingmodel：封包转辙模式hobbyist：n.业余爱好者WorldWideWeb：万维网Dot-combubble：网络泡沫上一页下一页返回TextB:HistoryoftheInternetNotes①Itisanetworkofnetworksthatconsistsofmillionsofprivate,public,academic,business,andgovernmentnetworksoflocaltoglobalscopethatarelinkedbyabroadarrayofelectronicandopticalnetworkingtechnologies.②Mosttraditionalcommunicationsmedia,suchastelephoneandtelevisionservices,arereshapedorredefinedusingthetechnologiesoftheInternet,givingrisetoservicessuchasVoiceoverInternetProtocol(VoIP)andIPTV.上一页下一页返回TextB:HistoryoftheInternet③ThisresearchandaperiodofcivilianfundingofanewU.S.backbonebytheNationalScienceFoundationspawnedworldwideparticipationinthedevelopmentofnewnetworkingtechnologiesandledtothecommercializationofaninternationalnetworkinthemid1990s,andresultedinthefollowingpopularizationofcountlessapplicationsinvirtuallyeveryaspectofmodernhumanlife.上一页下一页返回TextB:HistoryoftheInternet④TheseresearcheffortsincludedthoseofthelaboratoriesofDonaldDavies(NPL),PaulBaran(RANDCorporation),andLeonardKleinrockatMITandatUCLA.Theresearchledtothedevelopmentofseveralpacketswitchednetworkingsolutionsinthelate1960sand1970s,includingARPANETandtheX.25protocols.⑤Adoptionandinterconnectionoccurredquicklyacrosstheadvancedtelecommunicationnetworksofthewesternworld,andthenbegantopenetrateintotherestoftheworldasitbecamethedefactointernationalstandardfortheglobalnetwork.上一页返回GrammarFocus一、关系代词引导的定语从句

关系代词所代替的先行词是人或物的名词或代词，并在句中充当主语、宾语、定语等成分。关系代词在定语从句中作主语时，从句谓语动词的人称和数要和先行词保持一致。（1）who,whom,that。这些词代替的先行词是人的名词或代词，在从句中所起作用如下：Ishethemanwho/thatwantstoseeyou?他就是你想见的人吗？（who/that在从句中作主语）Heisthemanwhom/thatIsawyesterday.他就是我昨天见的那个人。（whom/that在从句中作宾语）下一页返回GrammarFocus（2)whose用来指人或物(只用作定语,若指物，它还可以同ofwhich互换）,例如：Theyrushedovertohelpthemanwhosecarhadbrokendown.

那人车坏了，大家都跑过去帮忙。Pleasepassmethebookwhose(ofwhich)coverisgreen.请递给我那本绿皮的书。上一页下一页返回GrammarFocus（3）which,that。它们所代替的先行词是事物的名词或代词，在从句中可作主语、宾语等，例如：

Aprosperitywhich/thathadneverbeenseenbeforeappearsinthecountryside.农村出现了前所未有的繁荣。（which/that在句中作宾语）

Thepackage(which/that)youarecarryingisabouttocomeunwrapped.

你拿的包快散了。(which/that在句中作宾语）上一页下一页返回GrammarFocus二、关系副词引导的定语从句关系副词可代替的先行词是时间、地点或理由的名词，在从句中作状语。（1）when,where,why。关系副词when,where,why的含义相当于“介词+which”结构，因此常常和“介词+which”结构交替使用（2）that代替关系副词。

that可以用于表示时间、地点、方式、理由的名词后取代when,where,why和“介词+which”引导的定语从句，在口语中that常被省略上一页下一页返回GrammarFocus三、判断关系代词与关系副词方法一：用关系代词，还是关系副词完全取决于从句中的谓语动词。及物动词后面无宾语，就必须要求用关系代词；而不及物动词则要求用关系副词。方法二：准确判断先行词在定语从句中的成分(主、谓、宾、定、状)，也能正确选择出关系代词/关系副词。上一页下一页返回GrammarFocus四、限制性和非限制性定语从句（1)定语从句有限制性和非限制性两种。限制性定语从句是先行词不可缺少的部分，去掉它主句意思往往不明确；非限制性定语从句是先行词的附加说明，去掉了也不会影响主句