资源描述：
《电子信息类专业英语第三章.ppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。
1、UnitThreeDataCommunicationsPassageADataCommunicationsPassageBCharacteristicsofCommunicationChannelsPassageCCommunicationEquipmentandSoftwarePassageADataCommunicationsTherapidgrowthofdatacommunicationshasbeeninfluencedprimarilybytheincreasingneedtomoveinformationtoandfromcomputers.Mo
2、derntime-sharedcomputerscancommunicatewithmanydatastationssimultaneously.Otherformsofdatatransmissionwhichthetelephoneandtelegraphlinesarecalledupontohandlearebatchdatatransmission,real-timetransmission(asinthecaseofairlinereservationsystems),bankingandcreditdata,man-computerconvers
3、ationwiththeaidofgraphics,datacollectionsystemsandautomaticmeterreading.Thecombinationofcomputersanddatacommunicationplacessuchnewrequirementsonthesystems,whichmusthandlethem,thatonecanrefertothembetterasteleprocessingratherthantelecommunications.[1]Teleprocessingstartedwiththeairli
4、nereservationsystems,wherethedistributionofcomputerdataisnotasimportantasthemaintenanceofaninventoryofseatsforthewholesystemandtheabilitytoaccesssuchaninventoryrapidlyatanumberofdistantpoints.Anotherexampleisthatofthebanks,whodesiredtocentralizetheiraccountingandprovideaccesstoacent
5、ralfileforalltheirbranches.Basically,therearethreereasonsforthedevelopmentofteleprocessingsystems:therequirementforcentralizedfiles,theneedtodistributecomputerservicesandtheadvantagegainedbyhavingflexibilityinlocationoftheoperatingstaffwhichutilizesthesystem.Initially,boththeairline
6、andbankingoperationscanbeestablishedonaprivatebasis,whichwouldminimizetheneedforswitchingoperations.Butinbothcases,theneedtoexpandbeyondprivateoperationssoonarises.Inthecaseoftheairlines,theneedarisestoaccessthefacilitiesofotherairlines;andinthecaseofthebanks,certaincommondatafacili
7、tiesmaybesharedwithotherbanks.Eventhoughprivatenetworksmaysufficeformanyservices,theneedtoprovidedatacommunicationsbetweenurbancentersleadstoregionalandnationalnetworks.IntheU.S.,theBellSystem,theindependenttelephonecompaniesandspecializeddatacommunicationnetworksareinvolvedascarrie
8、rsofsuchdata.Themos
