LTE典型信令过程

LTE典型信令过程2021/6/271 SoftwareArchitecture2021/6/2723类NAS信令流程1.会话管理相关2.位置管理相关3.鉴权管理相关2021/6/2732021/6/274UEeNBMMESGWPGWRRC:RRCConnectionsetupcompleteNAS:AttachRequestNAS:PDNconnectivityrequestS1AP:InitialUEmessageAuthenticationandNASsecurityprocedureHSSS6a:UpdateLocationrequestS6a:UpdateLocationanswerS11:CreatebearerrequestS5:CreatebearerrequestS5:CreatebearerresponseS11:CreatebearerresponseS1AP:InitialContextsetuprequestNAS:AttachacceptNAS:ActivateDefaultEPSbearerrequestNAS:AttachRequestNAS:PDNconnectivityrequestRRC:RRCConnectionReconfigurationNAS:AttachacceptNAS:ActivateDefaultEPSbearerrequestRRC:RRCConReconfigCompleteS1AP:InitialContextsetupresponseRRC:ULinformationTransferNAS:AttachcompleteNAS:ActivateDefaultEPSbeareracceptS1AP:UplinkNASTransportNAS:AttachcompleteNAS:ActivateDefaultEPSbeareraccept2021/6/275UEinitiatedDetachProcedureUEeNBMMESGWPGWHSSRRC:RRCConnectionsetupcompleteNAS:DetachrequestS1AP:InitialUEmessageNAS:DetachrequestAuthenticationandNASsecurityS11:DeletesessionrequestS5:DeletesessionrequestS5:DeletesessionresponseS11:DeletesessionresponseS1AP:DownlinkNAStransportNAS:DetachacceptRRC:DLInformationtransferNAS:DetachacceptRadioandS1ReleaseS6a:TDelaypurgetimerexpiresS6a:PurgeUErequestS6a:PurgeUEanswer2021/6/276UETriggeredServiceRequestProcedureInitialUEMessage2021/6/277NetworkTriggeredServiceRequest2021/6/278TAUprocedure2021/6/279InterMME-TAU-messageflow2021/6/2710Handover2021/6/2711HandoverAirInterfaceTYPESOFHANDOVERX2BasedHandover:withoutSGWchangeandwithSGWchange

S1BasedHandover:witheNB,MMEandSGWchange2021/6/2712X2HandoverX2istheinterfacebetweentwoeNB’sandX2-APistheprotocolsusedforcommunicationoverit.ThehandoverisdirectlyperformedbetweentwoeNodeB’s.HandovertakesplacewhentheeNBdetectsthatUEcannolongerbeservedbyitbecauseofthepowerconstraints.TheMMEisonlyinformedattheendofthehandoverprocedureoncethehandoverissuccessfulThereleaseofresourcesatthesourcesideisdirectlytriggeredfromthetargeteNB.2021/6/2713RRC:ConnectionReconfigurationRequestRRC:ConnectionReconfigurationCompleteUES-eNBT-eNBMMESGWRRC:MeasurementControlX2AP:HandoverRequestS11:ModifybearerrequestS11:ModifybearerresponseX2AP:SNStatusTransferSyncULAllocation+TAforUEULAllocationRRC:MeasurementReportHandoverDecisionX2AP:HandoverResponseUEDetachfromoldcellandsynctonewcellS1AP:PathSwitchRequestS1AP:PathSwitchResponseX2AP:UEContextReleaseEndMarkerSwitchDLPathDataForwardingDataForwardingEndMarkerFlushDLBuffer2021/6/2714S1HandoverThistypeofhandovertakesplacewhenthereisnoX2connectivitybetweensourceeNBandtargeteNB.BotheNB’sareservedbydifferentMME’s.SGW’scanalsobedifferent.SourceeNBisservedbysourceMMEandsourceSGWwhiletargeteNBisservedbytargetMMEandtargetSGW.SourceandtargetMME’scancommunicateoverS10interface.AllthehandoverdecisionsaretakingplaceonS1interface,itscalledasS1basedhandover.

2021/6/2715UET-eNBS-MMET-MMET-SGWS10:ForwardRelocationRequestS11:CreateSessionRequestS11:CreateSessionResponseS1AP:eNBStatusTransferS1AP:HandoverRequiredS1AP:HandoverRequestUEDetachfromoldcellandsynctonewcellS11:ModifyBearerRequestS1AP:UEContextReleaseCommandS-eNBS-SGWPGWHandoverDecisionS1AP:HandoverRequestAckS10:ForwardRelocationResponseS1AP:HandoverCommandRRC:ConnectionReconfigurationRRC:ConnectionReconfigurationCompleteS1AP:HandoverNotifyS11:ModifyBearerResponseS5:ModifyBearerRequestS1AP:UEContextReleaseCompleteS11:DeleteSessionRequestS11:DeleteSessionResponseS1AP:MMEStatusTransferS10:ForwardSRNSContextNotificationS10:ForwardSRNSContextAckS10:ForwardRelocationCompleteS10:ForwardRelocationCompleteAckS5:ModifyBearerResponse2021/6/2716开始2021/6/2717BeforetheUEcandoanything,aRadioResourceControlconnectionmustbeestablished.TheRRCisalogicalconnectionbetweentheUEandE-UTRAN.TherearetwodifferentRRCstates:RRCIDLERRCCONNECTED2021/6/2718RRCIDLEThisstateindicatesthatthereisnosignalingradiobearerisestablishedi.e.noRRCconnectionisestablished.TheUEisconsideredRRC_IDLEonceitobtainsthecenterfrequency,readsthetiminginformation,syncstotheeNodeB,andisreadytoreceivesystembroadcastinformation.UEmonitorsapagingchanneltodetectincomingcalls.UEcanperformsneighboringcellmeasurementsandmeasurementreporting.2021/6/2719RRCCONNECTEDThisstateindicatesthatthereissignalingradiobearerestablishedi.e.RRCconnectionisestablished.Transferofunicastdatato/fromanUE.TheUEMonitorscontrolchannelsassociatedwiththeshareddatachanneltodetermineifdataisscheduledforit.TheUEProvideschannelqualityandfeedbackinformation.TheUEPerformneighboringcellmeasurementsandmeasurementreporting.2021/6/2720RadioResourceControl(RRC)protocolstatesRRC_IDLEstatevs.RRC_CONNECTEDstate:UEdoesnothavecontextineNBandonlySignallingRadioBearer0(SRB0)isavailableforsignallingbetweeneNBandUE.UEhascontextineNBandcommunicationsbetweentheUEandthenetworkoccursonSignallingRadioBearer1(SRB1)andSignallingRadioBearer2(SRB2)UEgenerallyhasaniduniqueinthetrackingarea(S-TMSI=40bitslong);UEgenerallyhasaniduniqueintheeNBarea(C-RNTI=40bitslong)UEmayperformcellselection/reselectionwithoutinvolvementfromeNB;UEcanperformhandover(inter-eNB,intra-eNB,inter-RAT)undereNBcontrol;

UEcanrequestconnectionestablishmentorre-establishment;eNBprocessestheserequestsUEandeNBcantransmitand/orreceivedatato/fromeachother;UElistensforpagesatspecifictimes(DRX,configuredbyMME);onrequestfromtheMME,eNBsendspagestotheUEduringUE’sDRXupwaketimeAtPDCP/RLC/MAClevel:UEmonitorsL1/L2controlsignallingchanneltoseeifanytransmissionovertheshareddatachannelhasbeenallocatedtotheUEUEreportschannelqualityandfeedbackinformationtoeNBDRX/DTXperiodcanbeconfiguredaccordingtoUEactivitylevelforUEpowersavingandefficientresourceutilization.ThisisundercontrolofeNB(RRC).DRX=DiscontinuousReception;DTX=DiscontinuousTransmission2021/6/2721Controlplane:Radio-interfaceRelatedPHYMACRLCPDCPNASRRCPHYMACRLCPDCPRRCNASUEeNBMMEL1L2IPSCTPS1-APL1L2IPSCTPS1-APeNBMMES1-MMEL1L2IPSCTPX2-APL1L2IPSCTPX2-APeNBeNBX2-CNon-AccessStratum(NAS):ThekeycontrolinterfacebetweenMMEandUERadioResourceControl(RRC):ThemaincontrolinterfacebetweeneNBandUEPacketDataConvergenceProtocol(PDCP):Duplicatedetection,ROHCRadioLinkControl(RLC):Segmentation/re-assmebly,ARQ,acknowledgemode(AM)/un-acknowledgedmode(UAM),etcMediumAccessControl(MAC):AccessthechannelPhysicalLayer(PHY):Radiolayer,egmodulationetc.S1-AP:S1-ApplicationProtocolX2-AP:X2-ApplicationProtocolSCTP:StreamControlTransmissionProtocol2021/6/2722状态转换图2021/6/2723RRC连接建立过程2021/6/2724UEeNB1.RRC连接建立准备阶段RRCRRCRRCRRCRRCRRC2.CCCH:RRC连接请求3.CCCH:RRC连接建立4.DCCH:RRC连接建立完成RRC连接建立过程示意图2021/6/27251.准备阶段(1)UE用默认的物理信道参数来配置物理信道(2)UE为调度配置默认的半静态调度参数(3)UE配置默认的MAC主配置参数(4)UE配置CCCH参数(5)UE设置上行对齐定时器参数2.发RRC连接请求阶段(1)UE通过接入过程接入E-UTRAN,获得在UL_SCH信道上传数据的许可(2)设置UE标识(ue-Identity):S-TMSI或在0~240-1之间任选一个数(3)根据高层提供的RRC建立原因填写原因(establishmentCause信元)(4)通过PUSCH/UL_SCH/CCCH向E-UTRAN发RRC连接请求消息,消息中携带UE标识和建立原因3.接收响应阶段E-UTRAN通过PDSCH/DL_SCH/CCCH想UE发RRC连接建立消息。UE收到RRC连接建立消息后，根据消息中的信元进行以下操作：（1）根据radioResourceConfigDedicated信元进行无线资源配置过程（2）填写RRC连接建立完成消息4.设置完成阶段UE通过PUCH/UL_SCH/DCCH向E-UTRAN发RRC连接建立完成消息,进入RRC连接状态,结束本次RRC连接建立过程2021/6/2726

AnexampleofapossibleconnectionflowUEeNBMMEPowerON,measurements,cellselectionBCCH/BCH:MasterInformationBlockBCCH/BCH:SystemInformation(SIB-1)BCCH/BCH:SystemInformation(SIB-2)RACH:preamble_idPDCCH:ULgrantCCH:SRB0:RRCConnectionRequest(S-TMSI)CCH:SRB0:RRCConnectionSetup(S-TMSI,C-RNTI)DCCH:SRB1:RRCConnectionSetupComplete(C-RNTI,NAS_info)S1:INITIALUEMESSAGES1:INITIALCONTEXTSETUPREQUEST(UEcap)DCCH:SRB1:SecurityModeCommandDCCH:SRB1:SecurityModeCompleteDCCH:SRB1:RRCReconfigurationRequestDCCH:SRB1:RRCReconfigurationComplete2021/6/2727RandomAccessProcedure–ContentionBased(InitialAccessExample)ThefourstepsoftheRACHproceduresare:1) (MSG.1)RandomAccessPreambleonRACHinuplink:6bitstocarry:a5bitrandomID,and1bittoindicateinformationonsizeofmessage3limitedbyradioconditions.2) (MSG.2)RandomAccessResponseindownlink:semi-synchronous(withinaflexiblewindow)withmessage1;NoHARQ;SentonDL-SCH,andintendedforoneormultipleUEs3) (MSG.3)RRCConnectionRequestinuplink:UsesHARQ;RLCTM:nosegmentation;Ifthesizeofthemessageallowsit,theinitialNASmessage(orsomethingallowingtobuildtheinitialNASmessageineNB)canbeincluded;ConveysUEidentityatleastNASUEidentifier(initialaccess),orC-RNTI(othercases)4) (MSG.4)RRCContentionResolutiononDL-SCH:Notsynchronouswithmessage3.HARQisapplied;UEidentity,asprovidedinmessage3isechoedinRRCContentionResolutionmessageHARQfeedbackistransmittedonlybytheUEwhichdetectsitsownUEidentity2021/6/2728RRC连接释放过程由E-UTRAN发起,要求一个处于RRC连接状态的UE释放RRC连接,包括释放已建立的无线承载(RB)和所有无线资源RRC连接重配置过程E-UTRAN通过向UE发RRC连接重配置消息,发起RRC连接重配置过程。当要求建立，修改，释放RB，或进行切换，或建立，修改，释放测量时，使用RRC连接重配置过程来修改RRC连接。RRC连接重配置消息中包括测量配置，移动控制，无线资源配置（包括RB，MAC主配置和物理信道配置）等消息以及所有相关的专用NAS信息和安全配置信息。RRC连接重配置消息以及RRC连接重配置完成消息使用SRB1且承载在DCCH逻辑信道上2021/6/2729E-UTRAN附着2021/6/2730UEeNBMMESGWPGW1.RRC:RRCConnectionsetupcompleteNAS:AttachRequestNAS:PDNconnectivityrequest2.S1AP:InitialUEmessage3.AuthenticationandNASsecurityprocedureHSS4.S6a:UpdateLocationrequest5.S6a:UpdateLocationanswer6.S11:Createbearerrequest7.S5:Createbearerrequest8.S5:Createbearerresponse9.S11:Createbearerresponse10.S1AP:InitialContextsetuprequestNAS:AttachacceptNAS:ActivateDefaultEPSbearerrequestNAS:AttachRequestNAS:PDNconnectivityrequest11.RRC:RRCConnectionReconfigurationNAS:AttachacceptNAS:ActivateDefaultEPSbearerrequest12.RRC:RRCConReconfigComplete13.S1AP:InitialContextsetupresponse14.RRC:ULinformationTransferNAS:AttachcompleteNAS:ActivateDefaultEPSbeareraccept15.S1AP:UplinkNASTransportNAS:AttachcompleteNAS:ActivateDefaultEPSbeareraccept2021/6/2731UE附着到E-UTRAN中时，要建立一个默认的EPS承载，该承载使UE获得一个“总是在线”的IP连接1.UE发起附着过程，向eNodeB发一个RR消息（RRC连接配置完成消息），消息中携带高层的附着请求消息。包括以下参数：UE的IMSI，旧的GUTI以及附加GUTI：旧GUTI可以由P-TMSI和RAI(routingareaidentity)导出。如果UE没有一个有效的GUTI或P-TMSI，则必须提供IMSI；如果IMSI也没有，则必须提供ME的设备标识（IMEI）上一次访问的TAI：如果UE中保存有上一次访问的TAI，则应该把该参数提供给MMEUE核心网能力：描述UE的能力，包括支持的NAS和AS安全算法UE专用DRX参数：在接入过程中MAC为UE分配的DRX参数PDN类型：表示请求的IP地址类型（IPv4,IPv6,IPv4/IPv6)协议配置选项PCO：用于在UE和P-GW之间传输参数，比如UE希望的地址分配方式加密选项传输标志位附着类型：可以设为“切换”，“附着”，“紧急附着”KSIASME，NAS序列号，NAS-MAC此外，还携带两个RRC参数：被选网络，旧GUMMI2.eNodeB根据收到附着请求消息中的RRC参数进行配置,并向MME转发附着请求消息(通过S1AP消息:初始UE消息)2021/6/27323.身份ID请求和响应,NAS鉴权和安全功能激活,ME标识校验请求和确认4.MME向HSS发一个更新位置请求消息,告诉HSS目前在该MME中UE(由IMSI标识)正在发起附着5.HSS通过更新位置确认消息向MME提供该UE的签约数据(包括一个或多个PDN签约上下文)。MME正式确认UE驻留在某个TA中，并为该UE生成上下文6.MME向S-GW发生成默认承载请求消息,要求S-GW为该UE生成一个默认承载7.S-GW在其EPS承载列表中建立一个新的条目,并向P-GW发送生成默认承载请求消息,要求P-GW为该UE生成一个默认承载8.P-GW在其EPS承载列表中建立一个新的条目,开始在外部PDN网络和S-GW之间转发用户面PDU,并生成一个新的计费ID,开始计费。P-GW向S-GW发送默认承载建立响应消息，其中包含给UE分配的PDN地址9.S-GW向MME发默认承载建立响应消息,通知MME默认承载已经建立2021/6/273310.MME通知eNodeB(通过S1AP的初始上下问建立请求消息)UE的附着请求已经被接受,并要求建立一个初始上下文11.eNodeB通知UE附着请求已经被接受(通过RRC连接重配置消息)12.UE进行RRC连接重配置,完成后,向eNodeB回复一个RRC连接重配置完成消息13.eNodeB向MME回复一个初始上下文建立响应消息14.UE通过RRC的上行信息传输消息向eNodeB发一个NAS消息:附着完成消息,这标志着UE侧和附着相关的操作及设置已经完成15.eNodeB通过S1AP的上行NAS传输消息向MME转发UE的附着完成消息。本步后,一旦UE获得PDN地址,UE就想eNodeB发上行分组数据,这些分组数据可以通过隧道传到S-GW和P-GW更新承载请求及响应在MMES-GWP-GW之间完成后,EPS承载的E-UTRAN部分和EPC部分就连起来了,这时候下行分组数据也开始传送了2021/6/2734

会话管理过程UE和网络都能发起服务请求过程.UE发起的主呼,UE被叫以及网络发起ECM空闲态,UE的去附着都属于服务请求2021/6/2735UETriggeredServiceRequestProcedureInitialUEMessage2021/6/2736UE触发的服务请求过程(1)UE向MME发送服务请求消息(为NAS消息,封装在给eNodeB的RRC消息中,如上行信息传输消息或RRC连接建立完成消息)(2)eNodeB向MME转发该NAS消息(封装在S1AP的初始UE消息中,初试UE消息携带了服务小区的TAI和ECGI),如果MME不能处理服务请求,则会拒绝服务请求(3)NAS鉴权(4)MME通过S1AP向eNodeB发初始上下文建立请求消息,包含上行到S-GW的隧道端口号和地址,要求激活的所有EPS的S1承载和无线承载.(5)eNodeB发起无线承载建立过程(6)UE的上行链路数据通过eNode转发给S-GW(7)eNodeB通过S1AP向MME发初始上下文建立完成消息,其中携带下行到eNodeB的S1-U隧道端口号和地址(8)MME向S-GW发更新承载请求消息,告之下行的S1-UTEID和基站地址,以建立下行S1承载.MME从这一步开始能给UE传下行数据(9)如果RAT类型改变,S-GW还要向P-GW发更新承载请求消息(10)如果配置了PCC,P-GW要和PCRF交互获得不同的RAT的PCC规则,如果没有配置动态PCC,P-GW可以使用本地QoS策略(11)P-GW向S-GW回复更新承载响应消息(12)S-GW向MME回复更新承载响应消息2021/6/2737NetworkTriggeredServiceRequest2021/6/2738网络触发的服务请求当MME需要给在ECM空闲态的UE发消息,如进行MME/HSS发起的去附着过程,或有下行数据到达,要求S-GW生成或修改专用承载,在MME会发起网络触发的服务请求过程(1)当S-GW收到一个给UE的下行分组数据包,但S-GW的UE上下文中又没有下行用户面的TEID,表示当前没有和UE建立用户面连接,则S-GW缓存下行分组数据包,并查询目前服务UE的是哪个MME(SGSN)(2a)S-GW向MME(SGSN)发下行数据到达通知消息,请求用户面连接(2b)MME(SGSN)向S-GW发下行数据到达通知确认消息(3)如果UE注册到MME,则MME向UE注册TA的所有eNodeB发寻呼消息(4)如果eNodeB收到MME的寻呼消息,则开始寻呼UE(5)一旦收到E-UTRAN的寻呼消息,UE发起”UE触发的服务请求过程”(6)如果ISR是激活的,当E-UTRAN收到寻呼响应,S-GW向MME发停止寻呼消息2021/6/2739

切换过程2021/6/2740RRC连接状态的UE在E-UTRAN中进行移动的一般原则如下在E-UTRAN中,网络控制UE的移动,网络决定UE该进入哪个小区,哪个频点或哪个RAT。根据无线条件或负载情况等，网络会触发切换过程。在给UE发送切换消息之前，源eNodeB为切换准备一个或多个目标eNodeB。目标eNodeB生成用于进行切换的消息，消息中包括目标小区的接如层详细配置信息，源eNodeB把该消息透穿给UE。等合适的时候，源eNodeB发起DRB的转发。接到切换消息后，UE在第一个可用的RACH时刻就开始尝试接入到目标小区，也就是说，切换是异步的。因此，如果目标小区为这个随机接入分配了一个专用前缀（Preamble)，应该确保其在UE的第一个可能的RACH时刻就可用。一旦完成切换，UE给目标eNodeB发一个切换完成确认消息。源eNodeB中会保留UE的上下文一段时间，以防UE切换失败返回。检测到切换失败后，UE尝试在源小区或另一个也做好准备的小区使用RRC连接重建立过程，重新发起RRC连接。2021/6/2741RRC:ConnectionReconfigurationRequestRRC:ConnectionReconfigurationCompleteUES-eNBT-eNBMMESGWRRC:MeasurementControlX2AP:HandoverRequestS11:ModifybearerrequestS11:ModifybearerresponseX2AP:SNStatusTransferSyncULAllocation+TAforUEULAllocationRRC:MeasurementReportHandoverDecisionX2AP:HandoverResponseUEDetachfromoldcellandsynctonewcellS1AP:PathSwitchRequestS1AP:PathSwitchResponseX2AP:UEContextReleaseEndMarkerSwitchDLPathDataForwardingDataForwardingEndMarkerFlushDLBuffer2021/6/2742SourceeNBkeepsaskingUEforthepowermeasurementsinaRRCmeasurementcontrolmessage.UErespondswiththemeasurementsinRRCMeasurementReport.ThedetailsofthesemessagescanbefoundRRCprotocolspecification.BasedonthemeasurementreportsourceeNBtakesthedecisiontohandoverornot.IfthesourceeNBrealizesthatothereNBcanservebetter,thenitshallstartthehandoverprocedure.Ifthehandoverdecisionhasbeentaken,thensourceeNBsendsanX2-APmessageHandoverRequesttothetargeteNB.

TheHandoverRequestmayconsistofUEContextIEandE-RAB’s(E-UTRANRadioAccessBearer)tobesetup.UEcontextIEtypicallyconsistsofMMEinformation,UEsecuritycapabilitiesetc.E-RAB’stobesetuphasERABID,QoS,RRCcontextsetc.MultipleE-RAB’spertainingtomultipleEPSbearerscanbesentinthismessage.IfsendtheHandoverRequestAcktosourceeNB.TheAckincludestheERAB’sthathavebeenacceptedbythetargeteNB.

UponreceptionofHandoverRequestAckfromtargeteNB,sourceeNBsendsRRCConnectionReconfigurationmessagetoUE,toindicatethathandovershouldtakeplace.SourceeNBsendsSNStatusTransfermessagetotargeteNBtoindicatePDCPandHFNstatus.Atthismoment,UEdetachesfromsourceeNBandsyncswithtargeteNB.2021/6/2743UEcompletestheRRCreconfigurationbysendingRRCConnectionReconfigurationCompletemessagetotargeteNB.AndalsoUEstartstransmittingthedatatowardstargeteNB.ThisdataisbufferedattargeteNBuntiltheEPSBearershavebeenmodified.Next,targeteNBsendsanS1-APpatchSwitchRequestmessagetoMMEindicatingthathandoverhastakenplace.ThismessageincludestheERAB’sthathavebeenacceptedbytheeNB.MMEnowhastomodifytheEPSbearers,correspondingtoERAB’saccepted.MMEsendsModifybearerrequesttoSGW,whichincludesallEPSbearersthataretobemodifiedandalsothetargeteNB’sFTEID.SGW,ifrequestisaccepted,sendstheresponsealongwiththeS1-USGWFTEID,iftheyaremodified.MMEuponreceptionofModifyBearerResponsesendsPathSwitchRequestAcktotargeteNBindicatingthesuccessfulmodificationofEPSbearers.TargeteNBnowasksthesourceeNBtoreleaseallcontextsrelatedtotheUE.IfPMIPbasedS5/S8interfaceisconsidered,thentherewillbenomessageoverthatsameinterfaceforthishandoverscenario.2021/6/2744UET-eNBS-MMET-MMET-SGWS10:ForwardRelocationRequestS11:CreateSessionRequestS11:CreateSessionResponseS1AP:eNBStatusTransferS1AP:HandoverRequiredS1AP:HandoverRequestUEDetachfromoldcellandsynctonewcellS11:ModifyBearerRequestS1AP:UEContextReleaseCommandS-eNBS-SGWPGWHandoverDecisionS1AP:HandoverRequestAckS10:ForwardRelocationResponseS1AP:HandoverCommandRRC:ConnectionReconfigurationRRC:ConnectionReconfigurationCompleteS1AP:HandoverNotifyS11:ModifyBearerResponseS5:ModifyBearerRequestS1AP:UEContextReleaseCompleteS11:DeleteSessionRequestS11:DeleteSessionResponseS1AP:MMEStatusTransferS10:ForwardSRNSContextNotificationS10:ForwardSRNSContextAckS10:ForwardRelocationCompleteS10:ForwardRelocationCompleteAckS5:ModifyBearerResponse2021/6/2745SourceeNBtakesadecisiontohandovertheUEtotargeteNB.Irealizesthat,itdoesn’thaveaconnectivitywiththetargeteNB,soS1basedhandoverischosenforthispurpose.SourceeNBsendsS1APmessageHandoverRequiredtosourceMME,indicatedS1basedhandoverandthecauseforthehandover.ThismessageincludesMMEUES1APandeNBUES1APID.TheseID’sareusedtoidentifytheUEuniquelyinagiveneNBandMME.SourceMMEsendsGTPmessageForwardRelocationRequesttotargetMMEoverS10interfaceindicatingS1basedhandover.ThismessageincludesallthedetailsthatweresentwhentheUEwasattachedtotheEUTRAN.ThismessagealsoincludesalltheEPSbearercontextsthatwereestablishedforUE.AsthesameSGWisnotservingbothsourceandtargetMME’s,targetMMEsendsaGTPmessageCreateSessionRequesttotargetSGW.ThismessageincludesalltheEPSbearercontextsestablishedandalsoalltheinformationthatwassendduringinitialattach.(QoS,APN,PDNtypeetc).TargetSGW,ifaccepted,sendsaCreateSessionResponsetotargetMMEindicatingsuccess.TargetMMEthensendsS1APmessageHandoverRequesttotargeteNB.ThismessageincludestheE-RABcontextsthataretobeestablishedalongwithnewMMEUES1APID.ThehandovertypeissettoS1basedhandover.TargetMMErespondstothismessageHandoverRequestAck.ThisackincludestheERABcontextsadmitted.Inthenextstep,targetMMEsendsGTPmessageForwardRelocationResponsetosourceMMEindicatingthathandoverrequesthasbeenaccepted.ThisresponsealsoincludesalltheEPSbearersthathavebeenadmitted.2021/6/2746OncetheaboveresponseisreceivedbysourceMME,itsendsS1APmessageHandoverCommandtosourceeNBaskingittohandovertheUEtotargeteNB.SourceeNBforwardsthesametoUE.AfterthisUEbreaksfromoldcellandattachestonewcell.TargeteNBinformsthatUEhasattachedtoitbysendingHandoverNotifytotargetMMEoverS1interface.TargetMMEsendsGTPmessageModifyBearerRequesttotargetSGWindicatingtheneweNBFTEID.Targetacceptsthesame.SourceMMEaskssourceeNBtodeletealltheUEcontexts.AlsoitsendsdeletesessionrequesttosourceSGWaskingittodeletealltheEPSbearersforthatUE.2021/6/2747

跟踪区域更新过程2021/6/2748附着在E-UTRAN/EPC中的UE,当遇到下列情况是会触发跟踪区域更新过程TAU:(1)UE检测到它进入一个新的TA(该TA的TAI不在UE注册的TAI列表中)时(2)UE的周期性TA更新记时器过期时(3)在UTRAN的”PMM”连接态(如URA_PCH)的UE重选到E-UTRAN中时(4)在GPRS”READY”态的UE重选到E_UTRAN中时(5)TIN为”P-TMSI”的UE重选到E_UTRAN中时(6)当RRC连接因为”负载重平衡请求TAU”的原因被释放时(7)UE的核心网能力发生变化,或UE