《数据与计算机通信》PPT课件

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1、WilliamStallingsDataandComputerCommunications第15单元局域网概述Chapter15LocalAreaNetworkOverview115.1LANApplications(1)PersonalcomputerLANsLowcostLimiteddatarateBackendnetworksInterconnectinglargesystems(mainframesandlargestoragedevices)HighdatarateHighspeedinterfaceDistributedaccessLimited

2、distanceLimitednumberofdevices2LANApplications(2)StorageAreaNetworksSeparatenetworkhandlingstorageneedsDetachesstoragetasksfromspecificserversSharedstoragefacilityacrosshigh-speednetworkHarddisks,tapelibraries,CDarraysImprovedclient-serverstorageaccessDirectstoragetostoragecommunicat

3、ionforbackupHighspeedofficenetworksDesktopimageprocessingHighcapacitylocalstorageBackboneLANsInterconnectlowspeedlocalLANsReliabilityCapacityCost3StorageAreaNetworks4个人计算机局域网客户/服务器计算模式后端网络和存储区域网大型系统互联：大型机、海量存储特征：高速高可靠性、有限数量和距离高速办公室网络大信息量数据处理骨干局域网高带宽、高可靠性实现速率相对较低的LAN的互联局域网应用5后端网络与存储区域

4、网(1)大系统的互联大型机（Mainframes）巨型机（Supercomputers）海量存储设备（Massstoragedevices）主要需求小范围内有限数量的设备之间的批量数据传送典型特征高数据率高速接口分布式接入有限距离有限设备数量6后端网络与存储区域网(2)SAN–网络存储设备硬盘磁带库CD阵列715.2TopologiesandTransmissionmediumKeyelementsofaLANareTopologiesTransmissionmediumLayoutMediumaccesscontrol815.2.1TopologiesTree

5、BusSpecialcaseoftreeOnetrunk,nobranchesRingStar9LANTopologies10BusandTreeTopologyMultipointmediumTransmissionpropagatesthroughoutmediumHeardbyallstationsNeedtoidentifytargetstationEachstationhasuniqueaddressFullduplexconnectionbetweenstationandtapAllowsfortransmissionandreceptionNeed

6、toregulatetransmission需要规定传输Toavoidcollisions避免信号冲突Toavoidhogging(扰乱)避免信号混淆Datainsmallblocks-framesTerminatorabsorbsframesatendofmedium11FrameTransmissiononBusLAN12RingTopologyRepeatersjoinedbypointtopointlinksinclosedloopReceivedataononelinkandretransmitonanotherLinksunidirectionalS

7、tationsattachtorepeatersDatainframesCirculatepastallstationsDestinationrecognizesaddressandcopiesframeFramecirculatesbacktosourcewhereitisremovedMediaaccesscontroldetermineswhenstationcaninsertframe13FrameTransmissionRingLAN14StarTopologyEachstationconnecteddirectlytocentralnodeUsu

8、allyviatwopo