第6章+-移动IPv6技术

移动IPv6技术5-4学习内容和要求本讲学习内容及要求了解WLAN的基本知识了解移动通信的基本知识熟知移动IPv6技术相关术语掌握移动IPv6技术的工作原理掌握移动IPv6技术分析方法无线链路标准特性无线局域网无线局域网的基本概念1997年IEEE制定出适用有固定基础设施的无线局域网的协议IEEE802.11IEEE802.11很快也被ISO/IEC接纳为国际标准。无线局域网采用的无线传输介质主要是微波和红外线。采用微波的WLAN的调制方式主要是扩展频谱方式窄带调制方式WLAN的网络接口大都采用从数据链路层接入网络。无线网络不能代替有线网络，无线网络只能是有线网络的补充。无线局域网的发展免许可证频段IEEE802.11无线局域网IEEE802.11属于基于数据的无连接网络，提供常用的物理层和MAC层规范，能够改善所有无连接的应用，只要这种应用的网络层和运输层能够支持IEEE802.11的MAC层。TCP/IP协议簇中的TCP协议和IP协议是目前最主要的运输层和网络层协议，几乎所有的因特网的网络应用都可以通过TCP/IP协议在IEEE802.11的MAC层上直接运行。这就是说IEEE802.11不需要明确的规定服务的类型。有固定基础设施的无线局域网一个BSS可以是单独的（孤立的），也可以通过接入点AP连接到一个分配系统DS（DistributionSystem），通过DS再连接到一个BSS，这样可以构成一个扩展的服务集ESS（ExtendedServiceSet）。无固定基础设施的自组网络自组网络中站点之间的通信需要经过一些站点的转发，这些转发站点的作用类似于路由器，都具有路由器的功能。例如移动站源站点A和目的站点E通信，经过了一连串的转发过程，传输过程中途径的站点B、C、D是转发站点。IEEE802.11的协议体系结构对应传统的物理层分为三个子层：物理相关子层PWD（PhysicalMediumDependent）；物理层汇聚协议子层PLCP（PhysicalLayerConvergenceProtocol）；物理层管理子层。IEEE802.11的MAC层IEEE802.11标准设计了专用的MAC层，通过协调功能（CoordinationFunction）确定在基本服务集BSS中的移动站在什么时间可以发送或接收数据。IEEE802.11MAC层包括两个子层：一个称为分布协调功能DCF（DistributedCoordinationFunction）子层；另一个称为点协调功能PCF（PointCoordinationFunction）子层。无线网络基础（基础设施）networkinfrastructure基础设施模式basestation:connectsmobilesintowirednetworkhandoff:mobilechangesbasestationprovidingconnectionintowirednetwork无线网络基础（自组织）自主网络模式nobasestationsnodescanonlytransmittoothernodeswithinlinkcoveragenodesorganizethemselvesintoanetwork:routeamongthemselvesframecontroldurationaddress1address2address4address3payloadCRC22666260-23124seqcontrol802.11帧:寻址Address2:MACaddressofwirelesshostorAPtransmittingthisframeAddress1:MACaddressofwirelesshostorAPtoreceivethisframeAddress3:MACaddressofrouterinterfacetowhichAPisattachedAddress4:usedonlyinadhocmodeInternetrouterAPH1R1APMACaddrH1MACaddrR1MACaddraddress1address2address3802.11frameR1MACaddrAPMACaddrdest.addresssourceaddress802.3frame802.11frame:addressingframecontroldurationaddress1address2address4address3payloadCRC22666260-23124seqcontrolTypeFromAPSubtypeToAPMorefragWEPMoredataPowermgtRetryRsvdProtocolversion22411111111802.11frame:moredurationofreservedtransmissiontime(RTS/CTS)frameseq#(forreliableARQ)frametype(RTS,CTS,ACK,data)MobileSwitchingCenterPublictelephonenetwork,andInternetMobileSwitchingCenter蜂窝网体系结构概述connectscellstowideareanetmanagescallsetup(morelater!)handlesmobility(morelater!)MSCcoversgeographicalregionbasestation(BS)analogousto802.11APmobileusersattachtonetworkthroughBSair-interface:physicalandlinklayerprotocolbetweenmobileandBScellwirednetwork蜂窝网通信什么是移动?spectrumofmobility,fromthenetworkperspective:nomobilityhighmobilitymobilewirelessuser,usingsameaccesspointmobileuser,passingthroughmultipleaccesspointwhilemaintainingongoingconnections(likecellphone)mobileuser,connecting/disconnectingfromnetworkusingDHCP.移动:词汇和术语家乡网络homenetwork:permanent“home”ofmobile(e.g.,128.119.40/24)永久地址Permanentaddress:addressinhomenetwork,canalwaysbeusedtoreachmobilee.g.,128.119.40.186家乡代理homeagent:entitythatwillperformmobilityfunctionsonbehalfofmobile,whenmobileisremotewideareanetworkcorrespondent移动:词汇与术语关照地址Care-of-address:addressinvisitednetwork.(e.g.,79,129.13.2)wideareanetwork访问网络visitednetwork:networkinwhichmobilecurrentlyresides(e.g.,79.129.13/24)永久地址Permanentaddress:remainsconstant(e.g.,128.119.40.186)家乡代理homeagent:entityinvisitednetworkthatperformsmobilityfunctionsonbehalfofmobile.correspondent:wantstocommunicatewithmobileComponentsofcellularnetworkarchitecturecorrespondentMSCMSCMSCMSCMSCwiredpublictelephonenetworkdifferentcellularnetworks,operatedbydifferentprovidersrecall:蜂窝网络体系结构的元素蜂窝网络中的移动管理homenetwork:networkofcellularprovideryousubscribeto(e.g.,SprintPCS,Verizon)homelocationregister(HLR):databaseinhomenetworkcontainingpermanentcellphone#,profileinformation(services,preferences,billing),informationaboutcurrentlocation(couldbeinanothernetwork)visitednetwork:networkinwhichmobilecurrentlyresidesvisitorlocationregister(VLR):databasewithentryforeachusercurrentlyinnetworkcouldbehomenetworkPublicswitchedtelephonenetworkmobileuserhomeMobileSwitchingCenterHLRhomenetworkvisitednetworkcorrespondentMobileSwitchingCenterVLRGSM:移动的直接路由1callroutedtohomenetwork2homeMSCconsultsHLR,getsroamingnumberofmobileinvisitednetwork3homeMSCsetsup2ndlegofcalltoMSCinvisitednetwork4MSCinvisitednetworkcompletescallthroughbasestationtomobileMobileSwitchingCenterVLRoldBSSnewBSSoldroutingnewroutingGSM:切换(handoffwithcommonMSC)Handoffgoal:routecallvianewbasestation(withoutinterruption)reasonsforhandoff:strongersignalto/fromnewBSS(continuingconnectivity,lessbatterydrain)loadbalance:freeupchannelincurrentBSSGSMdoesn’tmandatewhytoperformhandoff(policy),onlyhow(mechanism)handoffinitiatedbyoldBSSGSM:handoffwithcommonMSC1.oldBSSinformsMSCofimpendinghandoff,provideslistof1+newBSSs2.MSCsetsuppath(allocatesresources)tonewBSS3.newBSSallocatesradiochannelforusebymobile4.newBSSsignalsMSC,oldBSS:ready5.oldBSStellsmobile:performhandofftonewBSS6.mobile,newBSSsignaltoactivatenewchannel7.mobilesignalsvianewBSStoMSC:handoffcomplete.MSCreroutescall8MSC-old-BSSresourcesreleasedMobil