A Seamless and Proactive End-to-End Mobility Solut

834IEEEJOURNALONSELECTEDAREASINCOMMUNICATIONS,VOL.22,NO.5,JUNE2004ASeamlessandProactiveEnd-to-EndMobilitySolutionforRoamingAcrossHeterogeneousWirelessNetworksChuanxiongGuo,Member,IEEE,ZihuaGuo,Member,IEEE,QianZhang,Member,IEEE,andWenwuZhu,SeniorMember,IEEEAbstract—Roamingacrossheterogeneouswirelessnetworkssuchaswirelesswideareanetwork(WWAN)andwirelesslocalareanetwork(WLAN)posesconsiderablechallenges,asitisusu-allydifficulttomaintaintheexistingconnectionsandguaranteethenecessaryquality-of-service.Thispaperproposesanovelseamlessandproactiveend-to-endmobilitymanagementsystem,whichcanmaintaintheconnectionsbasedontheend-to-endprinciplebyincorporatinganintelligentnetworkstatusdetectionmechanism.Theproposedsystemconsistsoftwocomponents,connectionmanager(CM)andvirtualconnectivity(VC).TheCM,byusingnovelmediaaccesscontrol-layerandphysical-layersensingtechniques,canobtainaccuratenetworkcondition,whileatthesametimereducingtheunnecessaryhandoffandping-pongeffect.TheVCcanmakemobilitytransparenttoapplicationswithoutadditionalnetwork-layerinfrastructuresupportusingalocalconnectiontranslation,andcanhandlemobilitywellinthenetworkaddresstranslatorandsimultaneousmovementcasesusingasubscription/notificationservice.Theproposedsystemenjoysseveraluniqueadvantages:1)capableofreactingtoroamingeventsproactivelyandaccurately;2)maintainingtheconnection’scontinuitywithsmallhandoffdelay;and3)beingaunifiedend-to-endapproachforbothIPv4andIPv6networks.Wehavebuiltaprototypesystemandperformedexperimentstodemonstratetheadvantagesoftheproposedsystem.IndexTerms—Mobilitymanagement,networkconditionde-tection,wirelesswideareanetwork(WWAN)/wirelesslocalareanetwork(WLAN)handoff.I.INTRODUCTIONWITHRAPIDdevelopmentanddeploymentofwirelesstechnologies,futurewirelessInternetisexpectedtocon-sistofdifferenttypesofwirelessnetworkswithdifferentaccessbandwidthandcoveragerange.Forinstance,wirelesslocalareanetworks(WLANs)canprovidehigh-speedInternetaccessatlimitedplaces(i.e.,hotspots),whereascellularnetworkscanofferuniversalnetworkaccessbutwithlimitedaccessrate.Anaturaltrendis,therefore,toutilizehigh-bandwidthprovidedbyWLANssuchasIEEE802.11andtheuniversalcoverageofthewirelesswideareanetworks(WWANs)suchasGeneralPacketRadioService(GPRS)/UniversalMobileTelecommuni-cationsSystem(UMTS)networks.It,therefore,requiresaneffi-cientsupportforswitchingbetweendifferentwirelessnetworks.ManuscriptreceivedJune7,2003;revisedDecember16,2003.TheauthorsarewiththeWirelessandNetworkingGroup,MicrosoftResearchAsia,Beijing100080,China(e-mail:[e-mail];[e-mail];[e-mail];[e-mail]).DigitalObjectIdentifier10.1109/JSAC.2004.826921Werefertosuchaswitchprocedureasinternetworkroamingorverticalhandoff.Oneofdesiredfeaturesforsuchheteroge-neouswirelessnetworksis,therefore,howtosupportseamlessandproactiveglobalroaming.Here,by“seamless,”wemeanthatupperlayerapplicationsshouldbeunawareoftheroamingeventsandtherelatedroamingprocedure.By“proactive,”wemeanthataccurateaccessnetworkconditionsanduserprefer-encesshouldbeobtainedinadvanceforaccurateroamingde-cision.Theseamlessandproactivefeaturescanenablemobileuserstomovefreelyacrossheterogeneouswirelessnetworkswiththeneededquality-of-service(QoS)requirement.Therehasbeenseveralworksfocusingonverticalhandoffsupport.In[1],Gustafssonetal.proposedthe“alwaysbestconnected(ABC)”conceptthatofferedconnectivityovermul-tiple-accesstechnologiestoenhanceuserexperience.ThisworkprovidedtheframeworkofABC;butmobilitymanagementwasnotdiscussed.In[2]–[4],severalexperimentalsystemswerere-ported,inwhichhandoffdecisionandconnectionmaintenanceissuesweretreatedseparatelyandthecoreofsuchsystemsisthemobilitymanagementscheme,whichcanmaintainusers’con-nectionsafteraverticalhandoffoccurred.However,inthesesys-tems,proactivenetworkconditiondetectionandseamlessmo-bilitymanagementwerenotaddressed.WeproposedamobilitymanagementschemesupportingWWANandWLANroamingin[5];however,technicaldetailssuchasnetworkbandwidthanddelayestimation,aswellasend-to-endmobilitymanagementwerenotfullyaddressed.Inordertoachieveseamlessandproactiveroaming,twokeyissueshavetobeaddressed:networkconditiondetectionforverticalhandoffdecisionandconnectionmaintenance.More-over,thenetworkconditiondetectionschemeandtheconnec-tionmaintenanceschemeneedtobetightlyintegratedtoformamobilitysystemforroamingacrossheterogeneouswirelessnet-works.Toachieveproactiveverticalhandoff,thenetworkcon-ditionshouldalwaysbeobtainablebyanappropriatehandoffmetric.Inheterogeneouswirelessnetworkenvironment,thisischallengingastheredoesnotexistcomparablesignalstrengthatthephysical-layertobeutilizedasverticalhandoffdecisionmetricsduetothedifferentphysicaltechniques.Thisisfur-thercomplicatedbythefactthatdifferentwirelessaccesstech-nologiesofferdifferentQoSparameterssuchasavailableac-cessbandwidthandaccessdelay,whichcouldbedifficulttoob-tain.Toachieveseamlessmobilitymanagement,smallhandoffdelayiscriticalandthemobilityeventshouldbemadetrans-parenttoapplications.Sinceminimizedhandoffdelaycanbe0733-8716/04$20.00©2004IE