LTE 切换信令流程.docx

LTE 切换信令流程.docx

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LTE切换信令流程

Handover

1Intra-E-UTRANhandover

1.1X2-basedhandover

1.1.1General

TheseproceduresareusedtohandoveraUEfromasourceeNodeBtoatargeteNodeBusingtheX2referencepoint.IntheseprocedurestheMMEisunchanged.TwoproceduresaredefineddependingonwhethertheServingGWisunchangedorisrelocated.InadditiontotheX2referencepointbetweenthesourceandtargeteNodeB,theproceduresrelyonthepresenceofS1-MMEreferencepointbetweentheMMEandthesourceeNodeBaswellasbetweentheMMEandthetargeteNodeB.

ThehandoverpreparationandexecutionphasesareperformedasspecifiedinTS 36.300 [5].IfemergencybearerservicesareongoingfortheUEhandovertothetargeteNodeBisperformedindependentoftheHandoverRestrictionList.TheMMEchecks,aspartoftheTrackingAreaUpdateintheexecutionphase,ifthehandoveristoarestrictedareaandifsoMMEreleasesthenon-emergencybearersasspecifiedinclause 5.10.3.

IftheservingPLMNchangesduringX2-basedhandover,thesourceeNodeBshallindicatetothetargeteNodeB（intheHandoverRestrictionList）thePLMNselectedtobethenewServingPLMN.

WhentheUEreceivesthehandovercommanditwillremoveanyEPSbearersforwhichitdidnotreceivethecorrespondingEPSradiobearersinthetargetcell.Aspartofhandoverexecution,downlinkandoptionallyalsouplinkpacketsareforwardedfromthesourceeNodeBtothetargeteNodeB.WhentheUEhasarrivedtothetargeteNodeB,downlinkdataforwardedfromthesourceeNodeBcanbesenttoit.UplinkdatafromtheUEcanbedeliveredviathe（source）ServingGWtothePDNGWoroptionallyforwardedfromthesourceeNodeBtothetargeteNodeB.OnlythehandovercompletionphaseisaffectedbyapotentialchangeoftheServingGW,thehandoverpreparationandexecutionphasesareidentical.

IftheMMEreceivesarejectiontoaNASprocedure（e.g.dedicatedbearerestablishment/modification/release;locationreportingcontrol;NASmessagetransfer;etc.）fromtheeNodeBwithanindicationthatanX2handoverisinprogress（seeTS 36.300 [5]）,theMMEshallreattemptthesameNASprocedureeitherwhenthehandoveriscompleteorthehandoverisdeemedtohavefailed,exceptincaseofServingGWrelocation.ThefailureisknownbyexpiryofthetimerguardingtheNASprocedure.

IfduringthehandoverproceduretheMMEdetectsthattheServingGWneedsberelocated,theMMEshallrejectanyPDNGWinitiatedEPSbearer（s）requestreceivedsincehandoverprocedurestartedandshallincludeanindicationthattherequesthasbeentemporarilyrejectedduetohandoverprocedureinprogress.TherejectionisforwardedbytheServingGWtothePDNGW,withthesameindication.

UponreceptionofarejectionforanEPSbearer（s）PDNGWinitiatedprocedurewithanindicationthattherequesthasbeentemporarilyrejectedduetohandoverprocedureinprogress,thePDNGWstartalocallyconfiguredguardtimer.ThePDNGWshallre-attempt,uptoapre-configurednumberoftimes,wheneitheritdetectsthatthehandoveriscompletedorhasfailedusingmessagereceptionoratexpiryoftheguardtimer.

IftheMMEreceivesarejectiontoaUEContextModificationRequestmessagewithaCSFallbackindicatorfromtheeNodeBwithanindicationthatanX2handoverisinprogress,theMMEshallresendaUEContextModificationRequestmessagewithCSFallbackindicatortothetargeteNodeBwhenthehandoveriscompleteortothesourceeNBwhenthehandoverisdeemedtohavefailed.

1.1.2X2-basedhandoverwithoutServingGWrelocation

ThisprocedureisusedtohandoveraUEfromasourceeNodeBtoatargeteNodeBusingX2whentheMMEisunchangedanddecidesthattheServingGWisalsounchanged.ThepresenceofIPconnectivitybetweentheServingGWandthesourceeNodeB,aswellasbetweentheServingGWandthetargeteNodeBisassumed.

Figure1.1.2-1:

X2-basedhandoverwithoutServingGWrelocation

NOTE 1:

ForaPMIP-basedS5/S8,proceduresteps（A）aredefinedinTS 23.402 [2].

1.ThetargeteNodeBsendsaPathSwitchRequestmessagetoMMEtoinformthattheUEhaschangedcell,includingtheTAI+ECGIofthetargetcellandthelistofEPSbearerstobeswitched.IfthetargetcellisaCSGcell,thetargeteNodeBincludestheCSGIDofthetargetcellinPathSwitchRequestmessage.Ifthetargetcellisinhybridmode,itincludestheCSGIDofthetargetcellandCSGAccessModesetto"hybrid"inthePathSwitchRequestmessage.TheMMEdeterminestheCSGmembershipbasedontheCSGIDandCSGAccessModereceivedfromthetargeteNodeB.TheMMEupdatestheUserCSGinformationbasedontheCSGIDandCSGAccessModereceivedfromthetargeteNodeBandCSGmembershipifoneoftheparametershaschanged.

NOTE 2:

X2handoverbetweenHeNBsispossiblewhenthehandoverisbetweenclosed/hybridaccessHeNBshavingthesameCSGIDorwhenthetargetHeNBisanopenaccessHeNB.

TheMMEdeterminesthattheServingGWcancontinuetoservetheUE

2.TheMMEsendsaModifyBearerRequest（eNodeBaddress（es）andTEIDsfordownlinkuserplanefortheacceptedEPSbearers,ISRActivated）messageperPDNconnectiontotheServingGWforeachPDNconnectionwherethedefaultbearerhasbeenacceptedbythetargeteNodeB.IfthePDNGWrequestedUE'slocationinfo,theMMEalsoincludestheUserLocationInformationIEinthismessage.IftheUETimeZonehaschanged,theMMEincludestheUETimeZoneIEinthismessage.IftheServingNetworkhaschanged,theMMEincludesthenewServingNetworkIEinthismessage.IfISRwasactivatedbeforethisprocedure,MMEshouldmaintainISR.TheUEisinformedabouttheISRstatusintheTrackingAreaUpdateprocedure.IftheServingGWsupportsModifyAccessBearersRequestprocedureandifthereisnoneedfortheSGWtosendthesignallingtothePGW,theMMEmaysendModifyAccessBearersRequest（eNodeBaddress（es）andTEIDsfordownlinkuserplanefortheacceptedEPSbearers,ISRActivated）perUEtotheServingGWtooptimizethesignalling.

IfthePDNGWrequestedUE'sUserCSGinformation（determinedfromtheUEcontext）,theMMEincludestheUserCSGInformationIEinthismessageiftheUserCSGInformationhaschanged.

TheMMEusesthelistofEPSbearerstobeswitched,receivedinstep 1,todeterminewhetheranydedicatedEPSbearersintheUEcontexthavenotbeenacceptedbythetargeteNodeB.TheMMEreleasesthenon-accepteddedicatedbearersbytriggeringthebearerreleaseprocedureasspecifiedinclause 5.4.4.2.IftheServingGWreceivesaDLpacketforanon-acceptedbearer,theServingGWdropstheDLpacketanddoesnotsendaDownlinkDataNotificationtotheMME.

IfthedefaultbearerofaPDNconnectionhasnotbeenacceptedbythetargeteNodeBandtherearemultiplePDNconnectionsactive,theMMEshallconsiderallbearersofthatPDNconnectionasfailedandreleasethatPDNconnectionbytriggeringtheMMErequestedPDNdisconnectionprocedurespecifiedinclause 5.10.3.

IfnoneofthedefaultEPSbearershavebeenacceptedbythetargeteNodeBorthereisaLIPAPDNconnectionthathasnotbeenreleased,theMMEshallactasspecifiedinstep 6.

3.IftheServingGWhasreceivedtheUserLocationInformationIEand/ortheUETimeZoneIEand/ortheServingNetworkIEand/orUserCSGInformationIEfromtheMMEinstep 2theServingGWinformsthePDNGW（s）aboutthisinformationthate.g.canbeusedforcharging,bysendingthemessageModifyBearerRequest（ServingGWAddressandTEID,UserLocationInformationIEand/orUETimeZoneIEand/orServingNetworkIEand/orUserCSGInformationIE）perPDNconnectiontothePDNGW（s）concerned.TheServingGWshallreturnaModifyBearerResponse（ServingGWaddressandTEIDforuplinktraffic）messagetotheMMEasaresponsetoaModifyBearerRequestmessage,oraModifyAccessBearersResponse（ServingGWaddressandTEIDforuplinktraffic）asaresponsetoaModifyAccessBearersRequestmessage.IftheServingGWcannotservetheMMERequestintheModifyAccessBearersRequestmessagewithoutS5/S8signallingorwithoutcorrespondingGxcsignallingwhenPMIPisusedovertheS5/S8interface,itshallrespondtotheMMEwithindicatingthatthemodificationsarenotlimitedtoS1-Ubearers,andtheMMEshallrepeatitsrequestusingModifyBearerRequestmessageperPDNconnection.

4.TheServingGWstartssendingdownlinkpacketstothetargeteNodeBusingthenewlyreceivedaddressandTEIDs.AModifyBearerResponsemessageissentbacktotheMME.

5.InordertoassistthereorderingfunctioninthetargeteNodeB,theServingGWshallsendoneormore"endmarker"packetsontheoldpathimmediatelyafterswitchingthepathasdefinedinTS 36.300 [5],clause 10.1.2.2.

6.TheMMEconfirmsthePathSwitchRequestmessagewiththePathSwitchRequestAckmessage.IftheUEAMBRischanged,e.g.alltheEPSbearerswhichareassociatedtothesameAPNarerejectedinthetargeteNodeB,theMMEshallprovidetheupdatedvalueofUEAMBRtothetargeteNodeBinthePathSwitchRequestAckmessage.

IfsomeEPSbearershavenotbeenswitchedsuccessfullyinthecorenetwork,theMMEshallindicateinthePathSwitchRequestAckmessagewhichbearersfailedtobeestablished（seemoredetailinTS 36.413 [36]）andfordedicatedbearersinitiatethebearerreleaseprocedureasspecifiedinclause 5.4.4.2toreleasethecorenetworkresourcesofthefaileddedicatedEPSbearers.ThetargeteNodeBshalldeletethecorrespondingbearercontextswhenitisinformedthatbearershavenotbeenestablishedinthecorenetwork.

IfnoneofthedefaultEPSbearershavebeenswitchedsuccessfullyinthecorenetworkoriftheyhavenotbeenacceptedbythetargeteNodeBortheLIPAPDNconnectionhasnotbeenreleased,