UESource Target MME/Serving eNBeNBEPCGW1.RRC Connection Reconfiguration0. Area Restriction Provided (Measurement Configuration)Packet dataPacket data2. Measurement Reports3. HO Decision4. Handover RequiredStart TS1RELOCprepINTER_ENB_S1_HO_PREPHO_EMG_PREP5. HO preparation in EPC6. Handover Request7. Admission Control and Resource Allocation8. Handover RequestStart TS1RELOCexecAcknowledge9. HO preparation Stop TS1RELOCprepcompletion in EPC9a. Create Indirect Data StartTS1RELOCOverall10. Handover CommandForwarding Tunnel Request11. Trigger HO execution9b. Create Indirect Data Forwarding Tunnel ResponseINTER_ENB_S1_HO_ATTHO_INTFREQ_ATT (HO_INTFREQ_GAP_ATT)HO_EMG_ATTHO_DRX_ATT12.RRC Connection Reconfiguration13a. eNB Status Transfer13b. MME Status TransferDetach from old cell(Indirect) Data ForwardingBuffer Packets from (Indirect) Data ForwardingSource eNB 14. Synchronisation14a. UL allocation + TA for UESee chapter 2.2.2.215. RRC Connection Reconfiguration CompleteStop TS1RELOCexecPacket data16. Handover Notify17a. Modify Bearer Request17b. Modify Bearer ResponseEnd Marker (or TDATAS1retard)Packet data (route optimized)Begin sending fresh S1-U dataStopTS118. UE Context Release CommandRELOCOverallINTER_ENB_S1_HO_SUCCRB_REL_REQ_NORM_REL*HO_INTFREQ_SUCC (HO_INTFREQ_GAP_SUCC)HO_EMG_SUCC20. Delete Indirect Data HO_DRX_SUCCForwarding Tunnel Request19. UE Context Release CompleteRelease data forwarding Release data forwarding 21. Delete Indirect Data resourcesresourcesForwarding Tunnel Response
3. 切换或基于测量的重定向到3G
终端需要支持异频测量和异系统互操作：
UE provides UE radio capabilities to eNB in RRC:UECapabilityInformation message which together with RRC:UECapabilityEnquiry is a part of UE capability transfer procedure described in 3GPP 36.331
? RRC:UECapabilityInformation message contains
IE:UE-CapabilityRAT-ContainerList which for E-UTRAN is encoded as IE:
noitarapePr revodnaHnoitucex ErevodnaHnoitelpmoC revodnaHUE-EUTRA-Capability
IE: UE-EUTRA-Capability contains two important information: ? IE: featureGroupIndicators
? FGI BIT22=true -> UTRAN measurements and reporting
? FGI BIT8=true -> EUTRA RRC_CONNECTED to UTRA CELL_DCH PS
handover
? IE: interRAT-Parameter
? provides information about TDS bands supported by the UE and they
should match with bands of TDS cells which are defined on LTE side as neighbor cell candidates
到3G的的切换是基于B2事件触发的。 MO Class LNHOT LNHOT Parameter Name Threshold1 UTRA for RSRP of serving cell Threshold2 RSCP for UTRA Neighbour cell b2Threshold2UtraRscp utra-RSCP b2Threshold1Utra b2-Threshold1 Abbreviated Name 3GPP name
到3G的重定向的流程：
UERNCGnGp SGSNE-UTRANRRC（MR：Event B1/B2）RRC Connection Release（Redirection）小区搜索、接收系统消息Random Access ProcessRAU RequestAuthentication / SecurityRAU AcceptRAU AcceptRAU CompleteRAU Complete
到3G的切换流程：
UEMR（Event B1/B2）Handover InitiationHandover RequiredForward Relocation RequestRelocation RequestRelocation Request AcknowledgeForward Relocation ResponseSource eNodeBTarget RNCSource MMETarget SGSNHO from E-UTRAN Command(MobilityFromE-UTRACommand)UTRAN Iu Access ProceduresHandover to UTRAN CompleteHandover CommandRelocation CompleteForward Relocation Complete NotificationForward Relocation Complete AcknowledgeRAU/TAU UpdateRelease Resources
4. NACC 或者SRVCC到2G
与切换到3G类似，也需要终端支持，主要是第9位和23位：
? FGI BIT23=true -> GERAN measurements, reporting and
measurement reporting event B2 in E-UTRA connected mode
? FGI BIT9=true -> EUTRA RRC_CONNECTED to GERAN
GSM_Dedicated handover
到3G的的切换是基于B2事件触发的： MO Class LNHOG LNHOG Parameter Name Threshold1 GERAN for RSRP of serving cell Threshold2 GERAN for RSSI neighbour cell b2Threshold2RssiGERAN b2-Threshold2GERAN b2Threshold1GERAN b2-Threshold1 Abbreviated Name 3GPP name 5. 盲重定向（R8）配置
在终端或系统不支持切换或者基于测量的重定向时选择R8重定向。R8重定向和CSFB 重定向的配置基本是一样的，其频率组可以共用，但是优先级可以分别设置。优先级的数字越大，级别越低。
一般建议重定向到3G，系统会把优先级最高的那个频点送给终端进行重选。
R8重定向也可以配置为不用优先级，即优先级都选择0，没有进行实验，怀疑系统随机选择一个频点下发给终端。
R8重定向的触发条件是服务小区的RSRP低于threshold-RSRP，触发前终端并不对异系统进行测量：
MO Class LNCEL Parameter Name Threshold th4 for RSRP Abbreviated Name threshold4 3GPP name threshold-RSRP threshold-RSRP是基于-140dBm的偏置值，建议-122dBm。可以与最小接入电平持平或者略高，防止在4G接入，一进入连接态就重定向到异系统。
盲重定向到3G的流程：
UERNCGnGp SGSNE-UTRANRRC（MR：Event A2）RRC Connection Release（Redirection）小区搜索、接收系统消息Random Access ProcessRAU RequestAuthentication / SecurityRAU AcceptRAU AcceptRAU CompleteRAU Complete