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Mobilitymanagementacrosshybridwirelessnetworks:TrendsandchallengesComputerCommunicationsFuturegenerationwirelessnetworksareenvisionedtobeacombinationofdiversebutcomplementaryaccesstechnologies.Internetworkingthesetypesofnetworkswillprovidemobileuserswithubiquitousconnectivityacrossawiderangeofnetworkingenvironments.Theintegrationofexistingandemergingheterogeneouswirelessnetworksrequiresthedesignofintelligenthandoffandlocationmanagementschemestoenablemobileuserstoswitchnetworkaccessandexperienceuninterruptedservicecontinuityanywhere,anytime.Realdeploymentofsuchmobilitystrategiesremainsasignificantchallenge.Inthisarticle,wefocusonhandoffmanagement.Wediscussindetailhandoffdecisionandimplementationproceduresandpresentrecenthandofftechniquesthataimatprovidingmobilityoverawiderangeofaccesstechnologies.Wealsodiscusssomeofthecapabilitiesofmobileterminalsthatarenecessarytoimplementseamlessmobilityoverhybridwirelessnetworks.Furthermore,wealsopresentanddiscusslimitationsofrecenthandoffdesignarchitecturesandprotocolsaswellasoutstandingchallengesthatstillneedtobeaddressedtoachieveportableandscalablehandoffsolutionsforcontinuousconnectivityacrosswirelessaccessnetworks.ArticleOutline1.Introduction2.Wirelessoverlaynetworks3.Handoffsinwirelessoverlaynetworks3.1.Horizontalvs.verticalhandoff3.2.Upward-verticalhandoffvs.downwardverticalhandoff3.3.Anticipatedvs.unanticipatedhandoff3.4.Hardvs.softhandoff3.5.Mobile-controlledhandoffvs.network-controlledhandoffvs.mobile-assistedhandoff4.Verticalhandoffprocess4.1.Networkdiscovery4.2.Handoffdecision:traditionalvs.nextgenerationhandoffstrategies4.3.Handoffmetricsinheterogeneousnetworks4.3.1.Cost4.3.2.Networkconditions4.3.3.Batterypower4.3.4.Applicationtypes4.3.5.Mobilenodeconditions4.3.6.Userpreferences4.4.Handoffimplementation4.4.1.Contexttransferforseamlesshandoffsinheterogeneouswirelessnetworks4.4.2.Candidateaccessrouterdiscoveryandcontexttransferprotocol4.4.3.CARDprotocol4.4.4.Contexttransferprotocol5.Terminalrequirementsforfutureheterogeneouswirelessnetworks5.1.Multimodewirelessterminals5.1.1.Requirementsformultimodeterminaloperation5.1.2.Deploymentissuesformultimodeterminals5.1.2.1.Networkdetection5.1.2.2.Networkinformation5.2.Software-definedradios5.2.1.MotivationforSDRdevelopment5.2.2.KeyfeaturesofSDRtechnology5.2.2.1.Reconfigurability5.2.2.2.Multimodeoperation5.2.2.3.Ubiquitousconnectivity5.2.2.4.Interoperability6.Recentverticalhandoffmanagementtechniquesproposedforheterogeneouswirelessnetworks6.1.MobileIP6.2.MobileIPv66.3.Networklayerhandoffapproaches6.3.1.HOPOVER6.3.1.1.HandoffPreparation6.3.1.2.Handoff6.3.1.3.UpdatingmobileIPinformation6.3.1.4.LimitationsofHOPOVER6.3.2.Hierarchicalapproach6.3.2.1.Limitationsofthehierarchicalapproach6.3.3.OmniCon6.3.3.1.LimitationsoftheOmniconApproach6.4.Transportlayerhandoffapproaches6.4.1.SCTP-basedverticalhandoff6.4.1.1.LimitationsofSCTP-basedhandoffscheme6.5.Applicationlayerhandoffapproach6.5.1.LimitationsofSIP6.6.Energy-efficientHandoffApproaches6.6.1.Adaptiveverticalhandoff6.6.2.WISE6.7.TCP-basedhandoffstrategies7.Researchchallengesformobilitymanagementinfutureheterogeneouswirelessnetworks7.1.Multimodality7.2.Efficientandseamlessroaming7.2.1.Detectionofnetworkcoverage7.2.2.Selectionofthemostappropriateaccessnetwork7.2.3.Handoffs7.3.Qualityofservice(QoS)7.3.1.QoSrequirements7.3.2.Security7.4.Billingandpricing7.5.Transferofcontextualinformation7.5.1.Contexttransfer7.5.2.Securityofcontexttransfer7.6.Inter-serviceprovidercompliance8.ConclusionWirelessmeshnetworks:asurveyComputerNetworksWirelessmeshnetworks(WMNs)consistofmeshroutersandmeshclients,wheremeshroutershaveminimalmobilityandformthebackboneofWMNs.Theyprovidenetworkaccessforbothmeshandconventionalclients.TheintegrationofWMNswithothernetworkssuchastheInternet,cellular,IEEE802.11,IEEE802.15,IEEE802.16,sensornetworks,etc.,canbeaccomplishedthroughthegatewayandbridgingfunctionsinthemeshrouters.Meshclientscanbeeitherstationaryormobile,andcanformaclientmeshnetworkamongthemselvesandwithmeshrouters.WMNsareanticipatedtoresolvethelimitationsandtosignificantlyimprovetheperformanceofadhocnetworks,wirelesslocalareanetworks(WLANs),wirelesspersonalareanetworks(WPANs),andwirelessmetropolitanareanetworks(WMANs).Theyareundergoingrapidprogressandinspiringnumerousdeployments.WMNswilldeliverwirelessservicesforalargevarietyofapplicationsinpersonal,local,campus,andmetropolitanareas.Despiterecentadvancesinwirelessmeshnetworking,manyresearchchallengesremaininallprotocollayers.ThispaperpresentsadetailedstudyonrecentadvancesandopenresearchissuesinWMNs.SystemarchitecturesandapplicationsofWMNsaredescribed,followedbydiscussingthecriticalfactorsinfluencingprotocoldesign.Theoreticalnetworkcapacityandthestate-of-the-artprotocolsforWMNsareexploredwithanobjectivetopointoutanumberofopenresearchissues.Finally,testbeds,industrialpractice,andcurrentstandardactivitiesrelatedtoWMNsarehighlighted.ArticleOutline1.Introduction2.Networkarchitecture3.Characteristics4.Applicationscenarios5.Criticalfactorsinfluencingnetworkperfo