信息网络通信基础

DataCommunications&Networking1.1Chapter1Introduction第一章绪论DepartmentofElectronicandCommunicationEngineeringNCEPUDataCommunications&Networking1.2DataCommunications&Networking1.3DataCommunications&Networking1.4DataCommunications&Networking1.5Chapter1Introduction绪论DataCommunications&Networking1.61-1DATACOMMUNICATIONS数据通信Thetermtelecommunicationmeanscommunicationatadistance.Theworddatareferstoinformationpresentedinwhateverformisagreeduponbythepartiescreatingandusingthedata.Datacommunicationsaretheexchangeofdatabetweentwodevicesviasomeformoftransmissionmediumsuchasawirecable.Components组成DataRepresentation数据表示DataFlow数据流Topicsdiscussedinthissection:DataCommunications&Networking1.7Datacommunicationsaretheexchangeofdatabetweentwodevicesviasomeformoftransmissionmediumsuchasawirecable.Theeffectivenessofadatacommunicationssystemdependsonfourfundamentalcharacteristics:1.Delivery.传递性Thesystemmustdeliverdatatothecorrectdestination2.Accuracy.准确性3.Timeliness.及时性4.Jitter.抖动性Jitterreferstothevariationinthepacketarrivaltime.(audioorvideo)DataCommunications&Networking1.8Figure1.1Fivecomponentsofdatacommunication1.Message报文2.Sender发送方3.Receiver接受方4.Medium介质5.Protocol协议DataCommunications&Networking1.9DataRepresentation数据表示•Text文本•Numbers数字•Images图像•Audio音频•Video视频DataCommunications&Networking1.10Figure1.2Dataflow(simplex,half-duplex,andfull-duplex)p6数据流分为单工、半双工和双工DataCommunications&Networking1.111-2NETWORKS网络Anetworkisasetofdevices(oftenreferredtoasnodes)connectedbycommunicationlinks.Anodecanbeacomputer,printer,oranyotherdevicecapableofsendingand/orreceivingdatageneratedbyothernodesonthenetwork.网络是指由介质链路连接在一起的一系列设备（常常被称为网络节点）DistributedProcessing分布式处理NetworkCriteria网络准则PhysicalStructures物理结构NetworkModels网络模型CategoriesofNetworks网络分类InterconnectionofNetworks:Internetwork网络互联：因特网Topicsdiscussedinthissection:DataCommunications&Networking1.121.2.1Distributedprocessing分布式处理Advantages:1.Security/encapsulation安全性/封装性2.Distributeddatabases分布式数据库3.Fasterproblemsolving更快的解决问题方式4.Securitythroughredundancy通过冗余达到安全性5.Collaborativeprocessing协作处理DataCommunications&Networking1.13安全性网络准则可靠性性能性能：多种形式衡量，包括传输时间和响应时间。性能取决于多种因素用户数量、传输介质类型、所连接的硬件能力以及软件效率可靠性：出现故障的频率、一条链路从故障恢复所花费的时间可靠性：保护数据免受未授权的访问1.2.2NetworkCriteria网络准则DataCommunications&Networking1.14Figure1.3Typesofconnections:point-to-pointandmultipoint点到点和多点ReservedcapacityVSSharedcapacity连接类型1.2.3物理结构PhysicalStructuresDataCommunications&Networking1.15Figure1.4Categoriesoftopology物理拓扑结构DataCommunications&Networking1.16Figure1.5Afullyconnectedmeshtopology(fivedevices)优点:1.专用线路dedicatedlinks2.健壮性robust3.秘密性、安全性privacy/security4.故障识别、排除faultidentification/isolation缺点：安装复杂，费用离谱DataCommunications&Networking1.17ExampleTheLuckyDuckyCorporationhasafullyconnectedmeshnetworkconsistingofeightdevices.Calculatethetotalnumberorcablelinksneededandthenumberofportsforeachdevices.SolutionNumberoflinks=n(n-1)/2=8(8-1)/2=28Numberofportsperdevice=n-1=8-1=7DataCommunications&Networking1.18Figure1.6AstartopologyconnectingfourstationsAdedicatedpoint-to-pointlinkonlytoacentralcontroller,hub星型拓扑用于局域网中，高速局域网通常用星型拓扑结构DataCommunications&Networking1.19Figure1.7AbustopologyconnectingthreestationsUsedinearlyEthernetLANsbuttheyarelesspupularnow.总线拓扑是多点配置的(multipoint)。Easeofinstallation;lesscabling;易安装，使用电缆最少，主缆能支持的抽头数和抽头之间的距离都有限制，在各个抽头处的信号反射会降低传输质量。健壮性差(robustness)引出线分接头DataCommunications&Networking1.20Figure1.8Aringtopologyconnectingsixstations被IBM引入令牌环局域网时曾盛行一时，目前要求高速局域网，这种拓扑结构就不流行了。Example1.2IfthedevicesinExample1.1areconfiguredasaringinsteadofamesh,howmanycablelinksarerequired.DataCommunications&Networking1.21Figure1.9Ahybridtopology混合:astarbackbonewiththreebusnetworksDataCommunications&Networking1.221.2.4NetworkModels网络模型OSI7-layermodelInternet5-layermodel1.2.5CategoriesofNetworks网络分类LocalAreaNetwork局域网WideAreaNetwork广域网MetropolitanAreaNetwork城域网InterconnectionofNetworks:Internetwork网络互联：因特网DataCommunications&Networking1.23Figure1.10AnisolatedLANconnecting12computerstoahubinacloset房间Currently,LANsizeislimitedtoafewkilometers.CommonLANtopologies:bus,ring,andstar.Speedsarenormally100or1000Mbps,wirelessLANsDataCommunications&Networking1.24Figure1.11WANs:aswitchedWANandapoint-to-pointWANWAN:X.25;ATMDataCommunications&Networking1.251.12AheterogeneousnetworkmadeoffourWANsandtwoLANsInternetworkheterogeneous不同种类的DataCommunications&Networking1.261-3THEINTERNET因特网TheInternethasrevolutionized彻底改变manyaspectsofourdailylives.Ithasaffectedthewaywedobusinessaswellasthewaywespendourleisuretime.TheInternetisacommunicationsystemthathasbroughtawealthofinformationtoourfingertipsandorganizeditforouruse.ABriefHistory历史简介TheInternetToday(ISPs)因特网现状（因特网服务提供商）Topicsdiscussedinthissection:DataCommunications&Networking1.27ARPA：AdvancedResearchProjectsAgency(美国国防部)高级计划研究署70年代初的美国深陷在越南战场的泥潭中，不能自拔，而国内的反战呼声一浪高过一浪。美国到了二战后第一个内外交困的年代。虽然这样，但是国内的各种科学技术还是在飞速地发展。ARPANET在不断地壮大。1970年的ARPANET已初具雏形，并且开始向非军用部门开放，许多大学和商业部门开始接入。但是它只有四台主机联网运行，甚至连局域网（LAN）的技术也还没有出现。当时用作接口机的HoneywellDDP516型小型机的内存只有12K。ARPANET在洛杉矶的加利福尼亚大学洛杉矶分校、加州大学圣巴巴拉分校、斯坦福大学、犹他州大学四所大学的4台大型计算机采用分组交换技术，通过专