网络与通信(chap7-Location Mibility Management(Mobile IP

1WirelessCommunicationandNetworkChapter7Location/MibilityManagement2Whydoweneedlocation/mobilitymanagement?Whatislocation/mobilitymanagement?TypesofmobilitymanagementHandoffmanagementLocationmanagementLocationManagementinGSMConceptofLocationareaLocationupdateprocedureCalldeliveryprocedureOtherlocationmanagementstrategiesLocationupdatePagingDatabasemanagementMobileIPmanagementWhatwewilllearninthischapter:3Whymobilitymanagement?Inwirelinenetworks,thereisafixedrelationshipbetweenaterminalanditsphysicallocationsIncontrast,mobileterminals(MT’s)arefreetotravelandthusitsnetworkaccesspointchangesasitmovesaroundthenetworkcoverageareaTheIDofanMTnolongerprovidesthecurrentlocationinformationoftheMT.Howtokeeptrackofmobileterminals?4Whymobilitymanagement?Anexample:cellularnetworkCaller’stelephonetunestothestrongestsignal.Caller’srequestincludesbothherandCallee’stelephonenumbers.BSrelaystherequesttotheswitch.TheswitchcommandsseveralBS’stotransitpagingmessagescontainingCallee’snumber.Callee’sphonerespondstothepagingmessagebyinformingthesystemofitslocation.TheswitchcommandsCaller’sphonetotunetochannelXandCallee’sphonetochannelY.Thecellularphoneconversationstarts.Duringtheconversation,Calleemovestoanewcell.Thesystemrearrangesitselftomaintaintheconversation.Whereis13520899790?Sendbroadcastmessagesfromeverybasestation?5Whatismobilitymanagement?MobilitymanagementisoneofthemostimportantandchallengingproblemsTheobjectiveisforthenetworktodeterminethelocationoftheMTatanytimeforbothmessagedeliveryandmaintainingconnectionsastheMTismovingintoanewareaMaintainlocationinformationasMTspower-on,move,orpower-offAfunctionatnetworklayerandabove6TypesofmobilitymanagementHandoffmanagement(keeptheconnection)Maintainauser’sconnectionastheMTcontinuestomoveandchangeitsaccesspointtothenetwork.Triggeredbyusermobility/roaming,signalstrengthdeterioration(弱化),trafficloadmanagement,etcLocationmanagement(establishthecommunication)TrackingthechangesoflocationsofMTs.DiscoveringthecurrentlocationoftheMTforcall/messagedelivery.7HandoffmanagementThreestagesInitiationEithertheuser,anetworkagent,orchangingnetworkconditionsidentifytheneedforhandoffNewconnectiongenerationThenetworkfindresourcesforthehandoffconnectionandperformanyadditionalroutingoperationsData-flowcontrolThenetworkmustmaintainthedeliveryofthedatafromtheoldconnectionpathtothenewconnectionpathaccordingtoagreed-upon(意见一致)serviceguarantees8LocationmanagementEverymobilenetworkmanageslocationinformationdifferentlydependingonseveralfactors:typeofofferedservice(calls,messages,etc..)subscriberdensitytrafficofmobileterminalcalls/messagesTwomainmethodsusedformobilitymanagement:methodswithoutlocationupdatingmethodsusinglocationareas9WithoutlocationupdatingNetworkdoesnotknowwheretheMTislocatedWheneveranincomingmessageorcallarrives,sendssearchingmessagesalloverthecoveredareas.TheadvantageissimplicityDisadvantages:LimitedcapacityforincomingcallsLimitedsubscriberdensitypopulation10UsinglocationareasLocationarea(LA)consistsofacertainnumberofcellsorsubnets.MTreportsitscurrentlocationareafromtimetotime-locationupdateNetworkalwaysknowsinwhichlocationareatheMTislocated(vialocationupdating),butitdoesnotknowpreciselywhatcell.Uponthearrivalofanincomingmessage,theMTissearchedonlyinsidethelocationarea.Limitsthecostofresourceutilizationduetolimitingthesearchingtothelocationarea.GSMusesthismethod.11LocationmanagementTwostagesLocationupdate(registration)MTnotifiesthenetworkofitsnewaccesspoint(e.g.,whenitispoweredon,ormovingintonewarea)NetworkauthenticatestheMTandrevisestheMT’slocation.Needlocationinformationstorage.MessagedeliveryNetworkisqueriedfortheMT’slocationprofileandthecurrentpositionoftheMTisfound.Message/callisdeliveredtothefoundlocation.12TwoMajorComponentsLocationUpdateThemobileterminalinformsthesystemitscurrentlocation.PagingThesystemsendsmessages(fromoneormorebasestations)tofindaparticularuser.13TwoExtremeCasesLocationneverupdate(nocost).Needtopageeverycells(highcost).Locationupdatesforeverycellcrossing(highcost).Needtopageonlyonecell(lowcost).Locationupdate14Partitiontheregionintodifferentlocationareas.LocationArea15LocationUpdateLA-1LA-2LocationupdateNolocationupdateLocationupdateisperformedwhenthereisaboundarycrossing.HowtodeterminethesizeofaLA?16LocationDatabasesHomeDatabaseEveryMSispermanentlyassociatedwithahomedatabaseKeeptrackoftheprofileoftheMSMobileID,authenticationkeys,location,etc.VisitingDatabaseKeepstrackoftheMSsinitsservicearea.ThesetwodatabasescommunicatewitheachothertoauthenticateandupdateeachotheraboutthelocationofanMS.GSMTerminology:HomeLocationRegister(HLR)VisitorLocationRegister(VLR)17MSCMSCVLRVLRHLR(1)(2)(3)(4)(6)(5)GSMExample:LocationUpdateMobileSwitchingCenter18LocationUpdateProcedures1.MStransmitsaLUtothenewBS2.TheBSforwardstheLUtotheMSC3.MSCsendsLUtotheHLRandupdatesVLR4.HLRdoesthefollowing:authenticatetheMSrecordtheIDofthenewVLRsendanACKtothenewVLR5.HLRsendsaregistrationcancellationmessagetotheoldVLR6.Theol