LTE典型信令過程

LTE典型信令過程2021/6/271 SoftwareArchitecture2021/6/2723類NAS信令流程1.會話管理相關2.位置管理相關3.鑒權(quán)管理相關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開始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狀態(tài)轉(zhuǎn)換圖2021/6/2723RRC連接建立過程2021/6/2724UEeNB1.RRC連接建立準備階段RRCRRCRRCRRCRRCRRC2.CCCH:RRC連接請求3.CCCH:RRC連接建立4.DCCH:RRC連接建立完成RRC連接建立過程示意圖2021/6/27251.準備階段(1)UE用默認的物理信道參數(shù)來配置物理信道(2)UE為調(diào)度配置默認的半靜態(tài)調(diào)度參數(shù)(3)UE配置默認的MAC主配置參數(shù)(4)UE配置CCCH參數(shù)(5)UE設置上行對齊定時器參數(shù)2.發(fā)RRC連接請求階段(1)UE通過接入過程接入E-UTRAN,獲得在UL_SCH信道上傳數(shù)據(jù)的許可(2)設置UE標識(ue-Identity):S-TMSI或在0~240-1之間任選一個數(shù)(3)根據(jù)高層提供的RRC建立原因填寫原因(establishmentCause信元)(4)通過PUSCH/UL_SCH/CCCH向E-UTRAN發(fā)RRC連接請求消息,消息中攜帶UE標識和建立原因3.接收響應階段E-UTRAN通過PDSCH/DL_SCH/CCCH想UE發(fā)RRC連接建立消息。UE收到RRC連接建立消息后，根據(jù)消息中的信元進行以下操作：（1）根據(jù)radioResourceConfigDedicated信元進行無線資源配置過程（2）填寫RRC連接建立完成消息4.設置完成階段UE通過PUCH/UL_SCH/DCCH向E-UTRAN發(fā)RRC連接建立完成消息,進入RRC連接狀態(tài),結(jié)束本次RRC連接建立過程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連接釋放過程由E-UTRAN發(fā)起,要求一個處于RRC連接狀態(tài)的UE釋放RRC連接,包括釋放已建立的無線承載(RB)和所有無線資源RRC連接重配置過程E-UTRAN通過向UE發(fā)RRC連接重配置消息,發(fā)起RRC連接重配置過程。當要求建立，修改，釋放RB，或進行切換，或建立，修改，釋放測量時，使用RRC連接重配置過程來修改RRC連接。RRC連接重配置消息中包括測量配置，移動控制，無線資源配置（包括RB，MAC主配置和物理信道配置）等消息以及所有相關的專用NAS信息和安全配置信息。RRC連接重配置消息以及RRC連接重配置完成消息使用SRB1且承載在DCCH邏輯信道上2021/6/2729E-UTRAN附著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附著到E-UTRAN中時，要建立一個默認的EPS承載，該承載使UE獲得一個“總是在線”的IP連接1.UE發(fā)起附著過程，向eNodeB發(fā)一個RR消息（RRC連接配置完成消息），消息中攜帶高層的附著請求消息。包括以下參數(shù)：UE的IMSI，舊的GUTI以及附加GUTI：舊GUTI可以由P-TMSI和RAI(routingareaidentity)導出。如果UE沒有一個有效的GUTI或P-TMSI，則必須提供IMSI；如果IMSI也沒有，則必須提供ME的設備標識（IMEI）上一次訪問的TAI：如果UE中保存有上一次訪問的TAI，則應該把該參數(shù)提供給MMEUE核心網(wǎng)能力：描述UE的能力，包括支持的NAS和AS安全算法UE專用DRX參數(shù)：在接入過程中MAC為UE分配的DRX參數(shù)PDN類型：表示請求的IP地址類型（IPv4,IPv6,IPv4/IPv6)協(xié)議配置選項PCO：用于在UE和P-GW之間傳輸參數(shù)，比如UE希望的地址分配方式加密選項傳輸標志位附著類型：可以設為“切換”，“附著”，“緊急附著”KSIASME，NAS序列號，NAS-MAC此外，還攜帶兩個RRC參數(shù)：被選網(wǎng)絡，舊GUMMI2.eNodeB根據(jù)收到附著請求消息中的RRC參數(shù)進行配置,并向MME轉(zhuǎn)發(fā)附著請求消息(通過S1AP消息:初始UE消息)2021/6/27323.身份ID請求和響應,NAS鑒權(quán)和安全功能激活,ME標識校驗請求和確認4.MME向HSS發(fā)一個更新位置請求消息,告訴HSS目前在該MME中UE(由IMSI標識)正在發(fā)起附著5.HSS通過更新位置確認消息向MME提供該UE的簽約數(shù)據(jù)(包括一個或多個PDN簽約上下文)。MME正式確認UE駐留在某個TA中，并為該UE生成上下文6.MME向S-GW發(fā)生成默認承載請求消息,要求S-GW為該UE生成一個默認承載7.S-GW在其EPS承載列表中建立一個新的條目,并向P-GW發(fā)送生成默認承載請求消息,要求P-GW為該UE生成一個默認承載8.P-GW在其EPS承載列表中建立一個新的條目,開始在外部PDN網(wǎng)絡和S-GW之間轉(zhuǎn)發(fā)用戶面PDU,并生成一個新的計費ID,開始計費。P-GW向S-GW發(fā)送默認承載建立響應消息，其中包含給UE分配的PDN地址9.S-GW向MME發(fā)默認承載建立響應消息,通知MME默認承載已經(jīng)建立2021/6/273310.MME通知eNodeB(通過S1AP的初始上下問建立請求消息)UE的附著請求已經(jīng)被接受,并要求建立一個初始上下文11.eNodeB通知UE附著請求已經(jīng)被接受(通過RRC連接重配置消息)12.UE進行RRC連接重配置,完成后,向eNodeB回復一個RRC連接重配置完成消息13.eNodeB向MME回復一個初始上下文建立響應消息14.UE通過RRC的上行信息傳輸消息向eNodeB發(fā)一個NAS消息:附著完成消息,這標志著UE側(cè)和附著相關的操作及設置已經(jīng)完成15.eNodeB通過S1AP的上行NAS傳輸消息向MME轉(zhuǎn)發(fā)UE的附著完成消息。本步后,一旦UE獲得PDN地址,UE就想eNodeB發(fā)上行分組數(shù)據(jù),這些分組數(shù)據(jù)可以通過隧道傳到S-GW和P-GW更新承載請求及響應在MMES-GWP-GW之間完成后,EPS承載的E-UTRAN部分和EPC部分就連起來了,這時候下行分組數(shù)據(jù)也開始傳送了2021/6/2734

會話管理過程UE和網(wǎng)絡都能發(fā)起服務請求過程.UE發(fā)起的主呼,UE被叫以及網(wǎng)絡發(fā)起ECM空閑態(tài),UE的去附著都屬于服務請求2021/6/2735UETriggeredServiceRequestProcedureInitialUEMessage2021/6/2736UE觸發(fā)的服務請求過程(1)UE向MME發(fā)送服務請求消息(為NAS消息,封裝在給eNodeB的RRC消息中,如上行信息傳輸消息或RRC連接建立完成消息)(2)eNodeB向MME轉(zhuǎn)發(fā)該NAS消息(封裝在S1AP的初始UE消息中,初試UE消息攜帶了服務小區(qū)的TAI和ECGI),如果MME不能處理服務請求,則會拒絕服務請求(3)NAS鑒權(quán)(4)MME通過S1AP向eNodeB發(fā)初始上下文建立請求消息,包含上行到S-GW的隧道端口號和地址,要求激活的所有EPS的S1承載和無線承載.(5)eNodeB發(fā)起無線承載建立過程(6)UE的上行鏈路數(shù)據(jù)通過eNode轉(zhuǎn)發(fā)給S-GW(7)eNodeB通過S1AP向MME發(fā)初始上下文建立完成消息,其中攜帶下行到eNodeB的S1-U隧道端口號和地址(8)MME向S-GW發(fā)更新承載請求消息,告之下行的S1-UTEID和基站地址,以建立下行S1承載.MME從這一步開始能給UE傳下行數(shù)據(jù)(9)如果RAT類型改變,S-GW還要向P-GW發(fā)更新承載請求消息(10)如果配置了PCC,P-GW要和PCRF交互獲得不同的RAT的PCC規(guī)則,如果沒有配置動態(tài)PCC,P-GW可以使用本地QoS策略(11)P-GW向S-GW回復更新承載響應消息(12)S-GW向MME回復更新承載響應消息2021/6/2737NetworkTriggeredServiceRequest2021/6/2738網(wǎng)絡觸發(fā)的服務請求當MME需要給在ECM空閑態(tài)的UE發(fā)消息,如進行MME/HSS發(fā)起的去附著過程,或有下行數(shù)據(jù)到達,要求S-GW生成或修改專用承載,在MME會發(fā)起網(wǎng)絡觸發(fā)的服務請求過程(1)當S-GW收到一個給UE的下行分組數(shù)據(jù)包,但S-GW的UE上下文中又沒有下行用戶面的TEID,表示當前沒有和UE建立用戶面連接,則S-GW緩存下行分組數(shù)據(jù)包,并查詢目前服務UE的是哪個MME(SGSN)(2a)S-GW向MME(SGSN)發(fā)下行數(shù)據(jù)到達通知消息,請求用戶面連接(2b)MME(SGSN)向S-GW發(fā)下行數(shù)據(jù)到達通知確認消息(3)如果UE注冊到MME,則MME向UE注冊TA的所有eNodeB發(fā)尋呼消息(4)如果eNodeB收到MME的尋呼消息,則開始尋呼UE(5)一旦收到E-UTRAN的尋呼消息,UE發(fā)起”UE觸發(fā)的服務請求過程”(6)如果ISR是激活的,當E-UTRAN收到尋呼響應,S-GW向MME發(fā)停止尋呼消息2021/6/2739

切換過程2021/6/2740RRC連接狀態(tài)的UE在E-UTRAN中進行移動的一般原則如下在E-UTRAN中,網(wǎng)絡控制UE的移動,網(wǎng)絡決定UE該進入哪個小區(qū),哪個頻點或哪個RAT。根據(jù)無線條件或負載情況等，網(wǎng)絡會觸發(fā)切換過程。在給UE發(fā)送切換消息之前，源eNodeB為切換準備一個或多個目標eNodeB。目標eNodeB生成用于進行切換的消息，消息中包括目標小區(qū)的接如層詳細配置信息，源eNodeB把該消息透穿給UE。等合適的時候，源eNodeB發(fā)起DRB的轉(zhuǎn)發(fā)。接到切換消息后，UE在第一個可用的RACH時刻就開始嘗試接入到目標小區(qū)，也就是說，切換是異步的。因此，如果目標小區(qū)為這個隨機接入分配了一個專用前綴（Preamble)，應該確保其在UE的第一個可能的RACH時刻就可用。一旦完成切換，UE給目標eNodeB發(fā)一個切換完成確認消息。源eNodeB中會保留UE的上下文一段時間，以防UE切換失敗返回。檢測到切換失敗后，UE嘗試在源小區(qū)或另一個也做好準備的小區(qū)使用RRC連接重建立過程，重新發(fā)起RRC連接。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

跟蹤區(qū)域更新過程2021/6/2748附著在E-UTRAN/EPC中的UE,當遇到下列情況是會觸發(fā)跟蹤區(qū)域更新過程TAU:(1)UE檢測到它進入一個新的TA(該TA的TAI不在UE注冊的TAI列表中)時(2)UE的周期性TA更新記時器過期時(3)在UTRAN的”PMM”連接態(tài)(如URA_PCH)的UE重選到E-UTRAN中時(4)在GPRS”READY”態(tài)的UE重選到E_UTRAN中時(5)TIN為”P-TMSI”的UE重選到E_UTRAN中時(6)當RRC連接因為”負載重平衡請求TAU”的原因被釋放時(7)UE的核心網(wǎng)能力發(fā)生變化,或UE