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1、Wireless Communication and NetworkChapter 7Location/Mibility Management1nWhydoweneedlocation/mobilitymanagement?nWhatislocation/mobilitymanagement?nTypesofmobilitymanagementnHandoffmanagementnLocationmanagementnLocationManagementinGSMnConceptofLocationareanLocationupdateprocedurenCalldeliveryprocedu
2、renOtherlocationmanagementstrategiesnLocationupdatenPagingnDatabasemanagementnMobileIPmanagementWhatwewilllearninthischapter:2Whymobilitymanagement?nIn wireline networks,there is a fixed relationship between a terminal and its physical locationsnIn contrast,mobile terminals(MTs)are free to travel an
3、d thus its network access point changes as it moves around the network coverage areanTheIDofanMTnolongerprovidesthecurrentlocationinformationoftheMT.nHow to keep track of mobile terminals?3Whymobilitymanagement?An example:cellular networknCallerstelephonetunestothestrongestsignal.nCallersrequestincl
4、udesbothherandCalleestelephonenumbers.BSrelaystherequesttotheswitch.nTheswitchcommandsseveralBSstotransitpagingmessagescontainingCalleesnumber.nCalleesphonerespondstothepagingmessagebyinformingthesystemofitslocation.nTheswitchcommandsCallersphonetotunetochannelXandCalleesphonetochannelY.nThecellular
5、phoneconversationstarts.nDuringtheconversation,Calleemovestoanewcell.Thesystemrearrangesitselftomaintaintheconversation.Where is 13520899790?Send broadcast messages from every base station?4Whatismobilitymanagement?nMobility management is one of the most important and challenging problemsnTheobjecti
6、veisforthenetworktodeterminethelocationoftheMTatanytimenforbothmessagedeliveryandmaintainingconnectionsastheMTismovingintoanewareanMaintain location information as MTs power-on,move,or power-offnA function at network layer and above5TypesofmobilitymanagementnHandoff management(keeptheconnection)nMai
7、ntainausersconnectionastheMTcontinuestomoveandchangeitsaccesspointtothenetwork.nTriggeredbyusermobility/roaming,signalstrengthdeterioration(弱化),trafficloadmanagement,etcnLocation management(establishthecommunication)nTrackingthechangesoflocationsofMTs.nDiscoveringthecurrentlocationoftheMTforcall/mes
8、sagedelivery.6HandoffmanagementnThree stagesnInitiationnEithertheuser,anetworkagent,orchangingnetworkconditionsidentifytheneedforhandoffnNew connection generationnThenetworkfindresourcesforthehandoffconnectionandperformanyadditionalroutingoperationsnData-flow controlnThenetworkmustmaintainthedeliver
9、yofthedatafromtheoldconnectionpathtothenewconnectionpathaccordingtoagreed-upon(意见一致)serviceguarantees7LocationmanagementnEvery mobile network manages location information differently depending on several factors:ntypeofofferedservice(calls,messages,etc.)nsubscriberdensityntrafficofmobileterminalcall
10、s/messagesnTwo main methods used for mobility management:nmethodswithoutlocationupdatingnmethodsusinglocationareas8WithoutlocationupdatingnNetwork does not know where the MT is locatednWhenever an incoming message or call arrives,sends searching messages all over the covered areas.nThe advantage is
11、simplicitynDisadvantages:nLimitedcapacityforincomingcallsnLimitedsubscriberdensitypopulation9UsinglocationareasnLocation area(LA)consists of a certain number of cells or subnets.nMTreportsitscurrentlocationareafromtimetotime-locationupdatenNetworkalwaysknowsinwhichlocationareatheMTislocated(vialocat
12、ionupdating),butitdoesnotknowpreciselywhatcell.nUpon the arrival of an incoming message,the MT is searched only inside the location area.nLimitsthecostofresourceutilizationduetolimitingthesearchingtothelocationarea.nGSM uses this method.10LocationmanagementnTwo stagesnLocation update(registration)nM
13、Tnotifiesthenetworkofitsnewaccesspoint(e.g.,whenitispoweredon,ormovingintonewarea)nNetworkauthenticatestheMTandrevisestheMTslocation.nNeedlocationinformationstorage.nMessage deliverynNetworkisqueriedfortheMTslocationprofileandthecurrentpositionoftheMTisfound.nMessage/callisdeliveredtothefoundlocatio
14、n.11TwoMajorComponentsnLocationUpdatenThemobileterminalinformsthesystemitscurrentlocation.nPagingnThesystemsendsmessages(fromoneormorebasestations)tofindaparticularuser.12TwoExtremeCasesLocation never update(no cost).Need to page every cells(high cost).Location updates for every cell crossing(high c
15、ost).Need to page only one cell(low cost).Location update13Partition the region into different location areas.LocationArea14LocationUpdateLA-1LA-2Location updateNo location updateLocation update is performed when there is a boundary crossing.How to determine the size of a LA?15LocationDatabasesnHome
16、 DatabasenEvery MS is permanently associated with a home databasenKeep track of the profile of the MSnMobile ID,authentication keys,location,etc.nVisiting DatabasenKeeps track of the MSs in its service area.These two databases communicate with each other to authenticate and update each other about t
17、he location of an MS.GSM Terminology:Home Location Register(HLR)Visitor Location Register(VLR)16MSCMSCVLRVLRHLR(1)(2)(3)(4)(6)(5)GSM Example:Location UpdateMobile Switching Center17LocationUpdateProcedures1.MStransmitsaLUtothenewBS2.TheBSforwardstheLUtotheMSC3.MSCsendsLUtotheHLRandupdatesVLR4.HLRdoe
18、sthefollowing:nauthenticatetheMSnrecordtheIDofthenewVLRnsendanACKtothenewVLR5.HLRsendsaregistrationcancellationmessagetotheoldVLR6.TheoldVLRremovestherecordoftheMSandreturnsanACKtoHLR18GSM Example:Call DeliveryMSCMSCVLRVLRHLR(1)(6)(4)(3)(2)(5)Mobile Switching CenterCalling MSCalled MS(7)19CallDelive
19、ryProcedure1.CallingMSsendsacallinitiationsignaltoMSCthroughBS.2.MSCsendsalocationrequesttoHLRofthecalledMS3.HLRdeterminesservingVLRofcalledMSandsendsarouterequestmessagetoit.4.MSCallocatesatemporaryIDtoMSandsendsthisIDtoHLR5.HLRforwardstheIDtoMSCofthecallingMS6.CallingMSCrequestsacallsetuptothecall
20、edMSC7.PagingmessagesaresenttocellswithintheLA.20OtherLocationManagementStrategies21Ping-PongEffectLA-1A lot of location updates may be generated if a user crosses LA boundary frequently.22OtherLocationUpdateAlgorithmsnTimeBasednEachuserperiodicallyupdateshislocation(e.g.everyhour)nMovementBasednEac
21、husercountsthenumberofboundarycrossingsbetweencells.nUpdateshislocationwhenthisnumberreachesapredefinedvalue,N.nDistanceBasednEachusertracksthedistancehehasmoved(innumberofcells)sincethelastupdate.nUpdateshislocationwhenthedistancereachesapredefinedvalue,N.23MovementBased(N=2)Location updateSuppose
22、location update is performed when entering this cell.24DistanceBased(N=2)Location updateSuppose location update is performed when entering this cell.25Page every cells within the LA.Blanket(地毯)Paging26Page the cells sequentially until the user is found.SequentialPaging1234876591027Howtodeterminepagi
23、ngorder?nMethod1:ShortestDistanceFirstnPagestheuserstartingfromthecellwherehelastupdatedhislocation.nMoveoutwardinashortest-distance-firstorder.nTiesarebrokenarbitrarily.nExample:(inahighway)Last Location Update1234528Howtodeterminepagingorder?nMethod2:BasedonLocationProbabilitynEstimatetheprobabili
24、tythatauserislocatedineachcellwithinthecurrentLA.nPagethecellsindecreasingorderofprobability.nExample:(inahighway)Last Location UpdateABCDESuppose Prob.Distribution is:0.05,0.2,0.4,0.25,0.1Paging order:C,D,B,E,A29PagingDelaynInourpreviousexample,theexpecteddelayisE D=0.41+0.252+0.23+0.14+0.051=1.95(
25、pagingcycles)nWorst-casedelayis5pagingcycles.nTheexpectednumberofcellstobepagedisalso1.95.nWorst-case:5cells.30BlanketPagingvs.SequentialPagingBlanketSequentialPagingcostLargeSmallPagingdelaySmallLargeSequential group paging may be used if there is a constraint on paging delay 31Page groups of cells
26、 sequentially until the user is found.SequentialGroupPaging1222333344Worst case delay is 4 cycles.32DatabaseManagementnLocationUpdatenInvolvestheupdatingoflocationdatabasesnCallDeliverynInvolvesthequeryingoflocationdatabasesnThecostisveryhighiftheMSislocatedfarawayfromitsHLR.ne.g.iftheMSisroaminginU
27、SAanditsHLRisinBeijing.33DatabaseManagementThreeEnhancementMethods:nPerUserLocationCachingnUserProfileReplicationnForwardingPointers34Per-UserLocationCachingnEverytimeuserxiscalled,xslocatoniscachedattheVLRinthecallersLA.nAnysubsequentcalltoxoriginatedfromthatLAcanreusethisinformation.nNoneedtoconta
28、ctuserxsHLR.35CacheInvalidationnEagerCachingnWheneverausermovestoanewLA,allcacheentriesforthisuserslocationareupdated.nLocationupdatecostincreasesifausermovesfrequently.nLazyCachingnCacheupdateisnotperformed.nTwocasescanoccur:ahitoramissnIncaseofamiss,ncontacttheHLRnthereisanadditionalcost,sincethec
29、achedVLRmustbevisitedfirst.36UserProfileReplicationnObservation:nEachuserusuallycommunicatesfrequentlywithasmallnumberofsources.nHowcanwemakeuseofthisobservation?nUserprofilesarereplicatedatselecteddatabasestoreducethecostofqueryingtheHLR.37UserProfileReplicationnWhenacallisinitiatedfromacertainLA,t
30、hecorrespondingMSCdeterminesifareplicationofthecalledMSsuserprofileisavailablelocally.nIfavailable,noHLRqueryisneeded.nWhentheMSmovestoanotherlocation,thenetworkupdatesallreplications.38PointerForwardingnEachtimeausermovestoanewLA,aforwardingpointerissetuptoitsperviousVLRtopointtothenewVLR.nCallstot
31、heuserwillfirstquerytheHLRtodeterminethefirstVLRandthenfollowthechaintoreachthecurrentVLR.nThelengthofthepointerchainislimitedtoamaximumvalueN.nThismethodcanreducethecostofupdatingtheHLR.39Mobile IP40OutlinenHowtosupportInternetmobility?nbyMobileIP.nOurdiscussionwillbebasedonIPv4(thecurrentversion).
32、41IPAddressnIPaddressisa32-bitnumberassignedtoeachnetworkinterfaceofanode.nNodes(suchasrouters)withmultiplenetworkinterfaceshavemultipleIPaddresses.IP Address in Dotted-Decimal Notation42NetworkPrefix;HostPortionnAnIPaddresshastwocomponentsnNetworkprefixnIdentifyingalinknIdenticalforallnodesattached
33、tothesamelinknHostportionnIdentifyingaspecifichostorrouterconnectedtothatlinknExample:129.61.18.26,prefixlength=24nNetworkprefix=129.61.18nHostportion=2643Motivations:nWithoutspecificsupport,messagedeliveryisnotpossibleformobilehosts(MHs)awayfromitshomeIPsubnet:nIProutingisbasedonthenetworkprefixand
34、destinationIPaddress:nExample:129.61.18.26,prefixlength=24nNetworkprefix=129.61.18nHostportion=26nMTcannotchangeIPaddressonmovingtonewIP-subnetotherwisenotabletodeliverymessages.44RoutingTableaRouter ARouter BRouter CHost 1Target/Prefix-LengthNext HopInterface7.7.7.99/32router1a7.7.7.0/24router2a0.0
35、.0.0/0router3aHost 1s routing tableHost 1 wants to forward a packet to 7.7.7.1Rules for Routing:1.Compare the left-most Prefix-Length bits of each Target with the IP destination address.2.Choose the matching route with the largest Prefix-Length.Default route451.0.0.11.0.0.21.0.0.2543.0.0.254aaac3.0.
36、0.2533.0.0.252cc2.0.0.2532.0.0.3b2.0.0.44.0.0.54.0.0.252bbbbHost 1Host 2Host 3Host 4Host 5Router ARouter BRouter CA Routing Example:1.0.0.1 2.0.0.4Target/Prefix-LengthNext HopInterface1.0.0.0/24“direct”a0.0.0.0/01.0.0.254aHost 1s routing tableEthernet ANetwork Prefix=1.0.0High-Speed Fiber BackboneNe
37、twork Prefix=3.0.0Ethernet BNetwork Prefix=2.0.0Ethernet CNetwork Prefix=4.0.0461.0.0.11.0.0.21.0.0.2543.0.0.254aaac3.0.0.2533.0.0.252cc2.0.0.2532.0.0.3b2.0.0.44.0.0.54.0.0.252bbbbHost 1Host 2Host 3Host 4Host 5Router ARouter BRouter CA Routing Example:1.0.0.1 2.0.0.4Target/Prefix-LengthNext HopInter
38、face1.0.0.0/24“direct”a3.0.0.0/24“direct”c2.0.0.0/243.0.0.253c4.0.0.0/243.0.0.252cRouter As routing tableEthernet ANetwork Prefix=1.0.0High-Speed Fiber BackboneNetwork Prefix=3.0.0Ethernet BNetwork Prefix=2.0.0Ethernet CNetwork Prefix=4.0.0471.0.0.11.0.0.21.0.0.2543.0.0.254aaac3.0.0.2533.0.0.252cc2.
39、0.0.2532.0.0.3b2.0.0.44.0.0.54.0.0.252bbbbHost 1Host 2Host 3Host 4Host 5Router ARouter BRouter CA Routing Example:1.0.0.1 2.0.0.4Target/Prefix-LengthNext HopInterface1.0.0.0/243.0.0.254c2.0.0.0/24“direct”b3.0.0.0/24“direct”cRouter Bs routing tableEthernet ANetwork Prefix=1.0.0High-Speed Fiber Backbo
40、neNetwork Prefix=3.0.0Ethernet BNetwork Prefix=2.0.0Ethernet CNetwork Prefix=4.0.0481.0.0.11.0.0.21.0.0.2543.0.0.254aaac3.0.0.2533.0.0.252cc2.0.0.2532.0.0.3b2.0.0.44.0.0.54.0.0.252bbbbHost 1Host 2Host 3Host 4Host 5Router ARouter BRouter CA Routing Example:1.0.0.1 2.0.0.4Target/Prefix-LengthNext HopI
41、nterface1.0.0.0/243.0.0.254c2.0.0.0/24“direct”b3.0.0.0/24“direct”cRouter Bs routing tableEthernet ANetwork Prefix=1.0.0High-Speed Fiber BackboneNetwork Prefix=3.0.0Ethernet BNetwork Prefix=2.0.0Ethernet CNetwork Prefix=4.0.0?49ProblemnThepacketisundeliverablenHost4isnotconnectedtoEthernetB.nRouterBw
42、illthensendaHost UnreachableerrormessagebacktoHost1.nQ:How to solve it?50Solution1:Host-SpecificRoutenPlacehost-specificroutesintheroutingtablesofRouterA,B,andCasfollows:Target/Prefix-LengthNext HopInterface2.0.0.4/323.0.0.252cTarget/Prefix-LengthNext HopInterface2.0.0.4/323.0.0.252cTarget/Prefix-Le
43、ngthNext HopInterface2.0.0.4/32“direct”bRouter ARouter BRouter CQ:Is this a good solution?51Solution2:ChangeIPAddressnSimplychangetheIPaddressofhost4,asitmovesfromEthernetBtoEthernetC.nForexample,DynamicHostConfigurationProtocol(DHCP)canbeusedtoacquireanewIPaddress.n这是我们通常使用的方式！nQ:Is this a good sol
44、ution?52Solution3:MobileIPnAstandardproposedtosolvetheproblemofInternetmobility.nItallowsthemobilenodetousetwoIPaddresses:nafixedhomeaddressnacare-ofaddressthatchangesateachnewpointofattachment53引入移动IP的原因n主机移动n接入位置的变化nIP变化n无法路由到原来的主机地址上n连接中断54移动IP的设计目标n移动节点在改变数据链路层接入点后，应能够保持与Internet上其它节点的连续通信n移动节点无
45、论连接到任何接入点，应该能够用原来的IP地址进行通信n移动节点应该能够与不具有移动IP的其它节点进行通信，并且不需要修改这些节点的协议n移动节点不应该比Internet上的其它节点面临更多的安全危险55移动IP的功能实体n移动节点（MobileNode）n家乡代理（HomeAgent）n外地代理（ForeignAgent）56MobileIPTerminology&Func.MNHAFACNInternetMN,Mobile NodeAn IP host that maintains network connectivity using its“home”IP address,regardle
46、ss of which subnet(or network)it is connected toFA,Foreign AgentProvides an addressable point of attachment to the MN called Care Of Address(COA)Maintains an awareness for all visiting MNsActs as a relay between the MN and its Home AgentReceives all packets for the MN from the MNs Home AgentHA,Home
47、AgentMaintains an association between the MNs“home”IP address and its care of address(loaned address)on the foreign networkRedirects and tunnels packets to the care of address on the foreign networkCN,Correspondent NodeDestination IP host in session with a Mobile NodeCOAMN57常用术语n家乡地址n转交地址n外地代理转交地址(F
48、oreignAgentCare-of-Address)n配置转交地址(CollocatedCare-of-Address)n家乡网络、家乡链路n外地网络、外地链路n通信对端节点n移动绑定58隧道(Tunnel)当一个数据包被封装在另一个数据包的净荷中进行传送时，所经过的路径称为隧道。图中还给出了一个例子，表明家乡代理为将数据包传送给移动节点，把数据包通过隧道先送给外地代理。59移动IP的工作机制1.通过周期地组播或广播一个称为代理广播（AgentAdvertisements）的消息，家乡代理和外地代理宣告它们与链路的连接关系。60移动IP的工作机制2.移动节点收到这些代理广播消息后，检查其中的
49、内容以确定自己是连在家乡链路还是外地链路上。当它连在家乡链路上时，移动节点就可像固定节点一样工作，即它不再利用移动IP的其他功能。61移动IP的工作机制下面的步骤假设移动节点连接在一条外地链路上。3.连在外地链路上的移动节点需要一个转交地址。它可以从外地代理广播的代理广播消息中找到外地代理转交地址，配置转交地址必须通过一个配置规程得到，比如用DHCP（DynamicHostConfigurationProtocol）、PPP的IPCP或手工配置。62移动IP的工作机制4.移动节点向家乡代理注册从第3步中得到的转交地址，可以通过移动IP中定义的消息交换来完成。在注册过程中，如果链路上有一个外地代
50、理，移动节点就向它请求服务。为阻止拒绝服务攻击，注册消息要求进行认证。63移动IP的工作机制5.家乡代理或者是在家乡链路上的其他一些路由器广播对移动节点家乡地址的网络前缀的可达性，从而吸引发往移动节点家乡地址的数据包，家乡代理截取这个包（可能用代理ARP），并根据移动节点在第4步中注册的转交地址，通过隧道将数据包传送给移动节点。6.在转交地址处可能是外地代理或移动节点的一个端口，原始数据包被从隧道中提取出来送给移动节点64移动IP的工作机制65MobileIPPacketForwardingnTrafficissentasusualtothehomesubnetnThehomeagentint