LTE-eSRVCC短板优化案例.docx

目录1概述12ESRVCC切换成功率指标介绍12.1eSRVCC指标统计信令节点22.2eSRVCC失败原因分析32.2.1LTE到GSM的切换出准备失败次数，目标侧准备失败32.2.2LTE到GSM的切换出准备失败次数，等待切换响应定时器超时52.2.3LTE到GSM的切换出准备失败次数，其它原因62.2.4LTE到GSM的切换出执行失败次数，源侧发生重建立72.2.5等待UE CONTEXT RELEASE消息超时102.2.6LTE到GSM的切换出执行失败次数，其他原因10概述SRVCC（Single Radio Voice Call Continuity）是3GPP提出的一种VoLTE语音业务连续性方案，主要是为了解决当单射频UE 在LTE/Pre-LTE 网络和2G CS 网络之间移动时，如何保证语音呼叫连续性的问题，即保证单射频UE 在IMS 控制的VoIP 语音和CS 域语音之间的平滑切换。LTE 网络建设初期，其覆盖范围有限，当用户在使用LTE 网络进行语音通话过程中，移动到LTE 信号较弱，但GERAN网络信号覆盖较好的区域时，为了保证语音呼叫连续性（Voice Call Continuity，VCC），需要将话路由LTE 切换到GERAN。由于目前还没有能够在LTE 和GERAN同时附着并收发数据的终端，因此LTE和2G 之前的业务连续性都基于Single Radio 模式，即双模单待方式。目前3GPP 已经制定出双模单待方式的语音业务连续性方案，即3GPP TS 23.216 R9中提出的双模单待无线语音呼叫连续性(Single Radio Voice Call Continuity，SRVCC）方案。1 eSRVCC切换成功率指标介绍eSRVCC切换成功率=切换至2G的切换成功次数（C373333312）/切换至2G的切换请求次数（C373333330）。其中：l 切换至2G的切换成功次数：源eNB接收到MME发送的“UE上下文释放”消息（UE CONTEXT RELEASE COMMAND），指示系统间（EUTRAN- GERAN）分组域切换执行成功。（3GPP TS36.413）l 切换至2G的切换请求次数：源eNB向MME发送的“切换请求”消息（HANDOVER REQUIRED），Handover Type IE（LTEtoGERAN）指示系统间（EUTRAN-GERAN）分组域切换请求。（3GPP TS36.413）1.1 eSRVCC指标统计信令节点失败原因对应计数器失败原因描述统计节点LTE到GSM的切换出准备失败次数，等待切换响应定时器超时C373333309源eNodeB等Handover Command消息定时器超时采样点4LTE到GSM的切换出准备失败次数，目标侧准备失败C373333310源eNodeB接收到从MME来的Handover Preparation failures消息采样点5LTE到GSM的切换出准备失败次数，其它原因C373333311源eNodeB在切换准备阶段发生除上述2种原因外其它失败采样点3LTE到GSM的切换出执行失败次数，源侧发生重建立C373333313在切换执行阶段源eNodeB收到RRC连接重建立请求消息采样点7LTE到GSM的切换出执行失败次数，等待UE CONTEXT RELEASE消息超时C373333314源eNodeB等待MME的Ue Context Release消息定时器超采样点8LTE到GSM的切换出执行失败次数，其他原因C373333315源eNodeB在切换执行阶段发生除上述原因外其它失败采样点91.2 eSRVCC失败原因分析eSRVCC切换分为切换准备阶段和切换执行阶段：切换准备阶段发生在Handover Required-Handover Command，切换执行阶段发生在MobilityFromEUTRA Command-Ue Context Realease Command。切换准备阶段为eNodeB -MME -eMSC -GSM基站之间的信令交互，和空口覆盖无关；切换执行阶段从采样节点来看只有MobilityFromEUTRA Command和LTE空口覆盖相关，当LTE下行覆盖较差（弱RSRP或弱RSRQ)时会增加UE接收MobilityFromEUTRA Command失败的概率从而造成eSRVCC失败，该原因造成的失败会统计到源eNodeB等待MME的Ue Context Release消息定时器超，其它的失败原因值和LTE覆盖、上行干扰、基站故障关系不大。1.2.1 LTE到GSM的切换出准备失败次数，目标侧准备失败TS36.413协议规定如果EPC或是目标侧不接受任何一个承载或是在切换准备阶段发生错误，MME会回复“handover Preparation failure”消息，eNode收到handover preparation failure消息后会统计到“目标侧准备失败”中。造成目标侧准备失败的主要原因包括：LTE侧GSM外部邻区参数配置、EPC参数配置错误、eMSC侧参数配置、GSM侧基站接纳失败、其它原因。 GSM外部邻区参数核查GSM外部邻区核查主要是和核查GSM CGI相关参数，在handover require中主要依靠CGI参数来进行目标侧寻址，如果CGI参数配置错误会导致核心网/GSM侧认为发生错误从而导致切换准备失败。CGI（Cell Global Indentfier）全球小区识别=MCC+MNC+LAC+CI需要重点核查：1、核查“管理网元-无线参数-TD-LTE-邻接小区配置-GERAN邻接小区”中“邻接小区所在的移动国家码”、“邻接小区所在的移动网络码”参数配置是否正确2、核查“管理网元-无线参数-TD-LTE-邻接小区配置-GERAN邻接小区”中的“位置区码”和小区标识的对应关系和GSM工参一致。 eMSC侧参数核查eMSC侧相关参数配置如下：1、eMSC检查eSRVCC相关控制开关和参数配置2、eMSC检查LAI和VMSC切换数据配置 EPC侧参数核查待补充。 GSM侧参数核查待补充。 其它原因排查流程切换准备涉及到LTE、核心网、GSM，在排查参数配置问题后可能需要核心网或GSM共同进行排查。TS23.216 6.2.2 规定了eSRVCC相关的信令流程，我们在做问题排查时依据相关的信令节点做问题定位排查，排查步骤如下：1、MME收到Handover Required后是否给eMSC发送了PS to CS Req，如果MME直接回复了Handover Preparation Failure，可能由于核心网参数配置或是核心网处理异常导致切换失败导致，需要核心网协助进行排查2、如果eMSC收到PS to CS Req之后回复的Handover Preparation Failure，则需要GSM协助进行排查1.2.2 LTE到GSM的切换出准备失败次数，等待切换响应定时器超时“管理网元-无线参数-TD-LTE-控制面定时器TDD”中“S1 HO时等待HO COMMAND的定时器(毫秒)”设置为10000ms（10s），在源侧发送Handover Required后再10s内未收到Handover Command命令造成eSRVCC切换失败。造成定时器超时的原因主要有：核心网/GSM侧参数配置错误导致核心网寻址错误；传输问题导致核心网/GSM侧未收到sRVCC相关信令；GSM基站故障未响应sRVCC切换命令。 参数核查1、LTE侧“管理网元-无线参数-TD-LTE-控制面定时器TDD- S1 HO时等待HO COMMAND的定时器(毫秒)”参数核查：确定参数配置为10000ms2、eMSC侧核查：VMSC检查和eMSC之间切换数据、VMSC检查LAI&CI和BSC关联数据配置 其它原因排查流程1、MME是否收到Handover Requied消息：如果MME未收到Handover Required消息，核查eNodeBMME之间的传输可靠性。核查方法：使用ems的“IP通道测试功能”检查eNodeBMME通道是否丢包，如果存在丢包的情况协调传输解决传输问题2、MME收到Handover Requied后是否向eMSC进行了Ps to Cs Req消息转发，如果MME未进行消息转发，协调MME共同进行排查3、eMSC是否收到Ps to Cs req消息，如果未收到核查MMEeMSC之间的传输4、eMSC收到Ps to Cs req后是否回复了Ps to Cs Rsp，如果未回复，协调GSM侧共同进行排查5、eMSC回复Ps to Cs Rsp后MME是否收到，如果未收到，核查MMEeMSC之间的传输6、MME收到Ps to Cs Rsp是否向eNodeB发送了Handover Command，如果未发送，协调MME共同进行排查7、MME发送Handover Command后eNodeB是否收到，如果未收到，核查eNodeBMME传输1.2.3 LTE到GSM的切换出准备失败次数，其它原因切换出准备失败，其它原因是指未收到MME发送的Handover preparation Failure，S1 HO时等待HO COMMAND的定时器也未超时，其它未知原因造成的失败，失败的原因可能有：eNodeB处理异常、MME/GSM处理异常、MME/GSM处理异常：类似于类似于在eNodeB发送Handover Required后，发起了UE Context Release Request造成sRVCCC切换失败。对于eNodeB处理异常的情况需要根据信令分析找出问题的根本原因。MME处理异常举例说明：类似于在eNodeB发送Handover Required后收到MME发送的UE Context Release Command命令造成sRVCC切换准备失败。对于MME处理异常的情况，根据信令分析情况联合核心网共同进行排查。总之准备失败的其它原因比较复杂，需要详细分析信令后再做进一步处理。1.2.4 LTE到GSM的切换出执行失败次数，源侧发生重建立在切换执行过程中源侧收到UE的rrc connection reestablishment request消息，源侧发起handover cancel造成切换失败。在eSRVCC切换执行阶段造成UE重建立的原因包括：无线链路失败、Mobility from eutra失败。 无线链路失败无线链路失败主要是由于LTE覆盖较差造成UE上行/下行失步，造成失步的原因主要是弱RSRQ、弱RSRQ、上行干扰、基站功率相关告警、测量时间过长造成切换延迟、切换准备阶段handover require-handover commad时延比较大造成切换延迟。目前版本sRVCC时参数默认配置为B2(LTE):-115dBm/B2(GSM):-95dBm，当下行干扰（mode3干扰、或重叠覆盖较高时），UE下行失步的概率较高，对于下行干扰严重区域，建议提高B2（LTE）门限降低下行失步的概率。参数配置路径参数名称默认值管理网元-无线参数-TD-LTE-测量参数配置-UE系统间测量参数测量配置号1012：语音B2 RSRP门限B2(LTE):-115dBm/B2(GSM):-95dBm上行干扰会造成上行失步UE进行重建，建议：（1）干扰排查（2）对于上行干扰站点可以尝试调整功控方式“闭环”-开环,同时修改P0_Nominal为-87-75基站功率相关告警包括：驻波告警、功率异常、RRU故障等告警测量时间长短和“测量参数-GERAN载频测量配置”相关，配置的冗余频点过多会增加UE检测时间，造成切换延迟，建议对GERAN载频进行精细优化切换准备阶段时延过大造成切换延迟，优化建议：（1）核查切换时延大原因，进行时延优化（2）提高B2（LTE）门限使切换提前 Mobility from eutra失败Mobiltyfromeutracommand失败原因包括：（1）T304超时 （2）在2G未能进行成功接入（3）UE和Mobiltyfrom eutracommand消息中部分内容不匹配Mobiltyfromeutracommand失败超时主要和邻区配置、GSM覆盖相关、特定UE、GSM侧未知故障等因素相关。邻区配置异常包括邻区漏配、邻区频点漏配、配置超远邻区。邻区漏配需要精细化的邻区优化来完成。邻区频点漏配是指“管理网元-无线参数-TD-LTE-邻接小区配置-GERAN邻接小区-BCCH载波的ARFCN”在“测量参数-GERAN载频测量配置”未配置造成部分邻区UE不测量从而影响eSRVCC切换成功率。优化建议核查“测量参数-GERAN载频测量配置”要包含所有“GERAN邻接小区-BCCH载波的ARFCN”。GSM覆盖：目标侧GSM信号质量差会造成GSM接入失败，目前版本默认B2(GSM):-95dBm，对于重建立失败较高的TOP小区适当提高B2（GSM）门限以保障在GSM侧能够正常接入。参数配置路径参数名称默认值管理网元-无线参数-TD-LTE-测量参数配置-UE系统间测量参数测量配置号1012：语音B2 RSRP门限B2(LTE):-115dBm/B2(GSM):-95dBm特定终端影响主要是指某个或某款终端在GSM侧接入异常导致。确定是否是某个终端导致切换异常可以通过（1）netmax切换智能分析可以基于“IMSI的汇总”来分析（2）通过汇总M-TMSI来进行分析；确定是否是某款终端导致同一通过“FGI（Feature Group ID）”汇总进行分析图 11 Netmax IMSI汇总图 12 M-TMSI信息查询图 13 FGI信息查询GSM侧未知故障造成UE在GSM接入异常，该问题需要跟踪GSM、LTE侧信令共同进行分析。1.2.5 等待UE CONTEXT RELEASE消息超时“S1源侧切换成功后等待MME释放定时器(毫秒)”配置为15s，eNodeB下发Mobilityform eutracommand”后15s内未收到MME的Uecontextreleasecommand，eNodeB会记录一次eSRVCC切换失败。造成超时的原因可能有：MME版本问题、传输问题、其它未知问题。MME版本问题：在R11之前的协议中未明确规定在eSRVCC切换完成后必须下发Uecontextreleasecommand。UE在sRVCC成功切换到GSM后，某些厂家的MME不下发Uecontextreleasecommand从而造成等待UE CONTEXT RELEASE消息。该问题优化建议：（1）MME版本升级（2）升级602版本后会对这部分进行TY，可以对这部分失败不做统计。传输问题由于传输丢包造成Uecontextreleasecommand未收到，该问题建议进行传输可靠性核查。其它未知问题分析：端到端信令进行分析。1.2.6 LTE到GSM的切换出执行失败次数，其他原因当eNodeB收到MME的Uecontextreleasecommand时，只有当里面携带的原因值为successful_handover才认为是sRVCC切换成功，所有其它携带的原因值都认为是执行失败造成命令携带其它原因值的原因有：中兴MME版本、其它原因 中兴MME版本问题中兴MME在R11之前的版本中eSRVCC切换完成后，核心网下发UE CONTEXT REALEASE COMMAND，携带的原因值为TS1AP_CauseNAS_Root_normal_release。根据TS36.413 ，当切换成功导致的上下文释放，携带的原因值应该为Handover Success而不是Normal Release。网管目前统计eNB eSRVCC切换执行成功也是统计源eNB接收到MME发送的“UE上下文释放”消息（UE CONTEXT RELEASE COMMAND），释放原因是“handover success”。目前MME V4.10.18已经取得入网证并在全网进行升级，对于未升级的区域建议尽快进行MME版本升级。 其它原因详见附录A，释放原因说明。需要根据UE CONTEXT RELEASE COMMAND携带的原因值再进行进一步的定位。在P02版本中计划对其它原因造成的失败进行TY，按照原因值分为4个开关：Normal Release、Release due to E-UTRAN Generated Reason、Failure in the Radio Interface Procedure、其它所有原因，4个开关可以通关B类参数进行控制，可以根据优化需求有选择性的关闭其中某个或全部失败原因值的统计。附录A 释放原因说明（TS36.413 ）IE/Group NamePresenceRangeIE Type and ReferenceSemantics DescriptionCHOICE Cause GroupMRadio Network LayerRadio Network Layer Cause MENUMERATED(Unspecified,TX2RELOCOverall Expiry, Successful Handover,Release due to E-UTRAN Generated Reason, Handover Cancelled, Partial Handover, Handover Failure In Target EPC/eNB Or Target System,Handover Target not allowed,TS1RELOCoverall Expiry,TS1RELOCprep Expiry,Cell not available,Unknown Target ID,No Radio Resources Available in Target Cell, Unknown or already allocated MME UE S1AP ID,Unknown or already allocated eNB UE S1AP ID,Unknown or inconsistent pair of UE S1AP ID, Handover desirable for radio reasons,Time critical handover,Resource optimisation handover,Reduce load in serving cell, User inactivity,Radio Connection With UE Lost, Load Balancing TAU Required, CS Fallback Triggered,UE Not Available For PS Service, Radio resources not available,Failure in the Radio Interface Procedure, Invalid QoS combination, Inter-RAT redirection,Interaction with other procedure, Unknown E-RAB ID, Multiple E-RAB ID instances, Encryption and/or integrity protection algorithms not supported, S1 intra system Handover triggered, S1 inter system Handover triggered, X2 Handover triggered,Redirection towards 1xRTT,Not supported QCI value,invalid CSG Id)Transport LayerTransport Layer CauseMENUMERATED(Transport Resource Unavailable,Unspecified,)NASNAS CauseMENUMERATED (Normal Release,Authentication failure,Detach,Unspecified, ,CSG Subscription Expiry)ProtocolProtocol CauseMENUMERATED(Transfer Syntax Error,Abstract Syntax Error (Reject),Abstract Syntax Error (Ignore and Notify),Message not Compatible with Receiver State,Semantic Error,Abstract Syntax Error (Falsely Constructed Message), Unspecified, )MiscMiscellaneous CauseMENUMERATED(Control Processing Overload, Not enough User Plane Processing Resources,Hardware Failure,O&M Intervention,Unspecified, Unknown PLMN, )The meaning of the different cause values is described in the following table. In general, “not supported” cause values indicate that the related capability is missing. On the other hand, “not available” cause values indicate that the related capability is present, but insufficient resources were available to perform the requested action.Radio Network Layer causeMeaningUnspecifiedSent for radio network layer cause when none of the specified cause values applies.TX2RELOCOverall Expiry The timer guarding the handover that takes place over X2 has abnormally expired.Successful HandoverSuccessful handover.Release due to E-UTRAN generated reasonRelease is initiated due to E-UTRAN generated reason.Handover CancelledThe reason for the action is cancellation of Handover.Partial HandoverProvides a reason for the handover cancellation. The HANDOVER COMMAND message from MME contained E-RABs to Release List IE and the source eNB estimated service continuity for the UE would be better by not proceeding with handover towards this particular target eNB.Handover Failure In Target EPC/eNB Or Target SystemThe handover failed due to a failure in target EPC/eNB or target system.Handover Target not allowedHandover to the indicated target cell is not allowed for the UE in question.TS1RELOCoverall ExpiryThe reason for the action is expiry of timer TS1RELOCoverall.TS1RELOCprep ExpiryHandover Preparation procedure is cancelled when timer TS1RELOCprep expires.Cell not availableThe concerned cell is not available.Unknown Target IDHandover rejected because the target ID is not known to the EPC.No radio resources available in target cellLoad on target cell is too high.Unknown or already allocated MME UE S1AP IDThe action failed because the MME UE S1AP ID is either unknown, or (for a first message received at the eNB) is known and already allocated to an existing context.Unknown or already allocated eNB UE S1AP IDThe action failed because the eNB UE S1AP ID is either unknown, or (for a first message received at the MME) is known and already allocated to an existing context.Unknown or inconsistent pair of UE S1AP IDThe action failed because both UE S1AP IDs are unknown, or are known but do not define a single UE context.Handover Desirable for Radio ReasonsThe reason for requesting handover is radio related.Time Critical HandoverHandover is requested for time critical reason i.e., this cause value is reserved to represent all critical cases where the connection is likely to be dropped if handover is not performed.Resource Optimisation HandoverThe reason for requesting handover is to improve the load distribution with the neighbour cells.Reduce Load in Serving CellLoad on serving cell needs to be reduced. When applied to handover preparation, it indicates the handover is triggered due to load balancing.User InactivityThe action is requested due to user inactivity on all E-RABs, e.g., S1 is requested to be released in order to optimise the radio resources.Radio Connection With UE LostThe action is requested due to losing the radio connection to the UE.Load Balancing TAU RequiredThe action is requested for all load balancing and offload cases in the MME.CS Fallback triggeredThe action is due to a CS fallback that has been triggered. When it is included in UE CONTEXT RELEASE REQUEST message, it indicates the PS service suspension is not required in the EPC.UE Not Available for PS ServiceThe action is requested due to a CS fallback to GERAN that has been triggered.When it is included in the UE CONTEXT RELEASE REQUEST message, it indicates that the PS service suspension is required in the EPC due to the target GERAN cell or the UE has no DTM capability.Radio resources not availableNo requested radio resources are available.Invalid QoS combinationThe action was failed because of invalid QoS combination. Inter-RAT RedirectionThe release is requested due to inter-RAT redirection. When it is included in UE CONTEXT RELEASE REQUEST message, it indicates the PS service suspension is not required in the EPC.Failure in the Radio Interface ProcedureRadio interface procedure has failed.Interaction with other procedureThe action is due to an ongoing interaction with another procedure.Unknown E-RAB IDThe action failed because the E-RAB ID is unknown in the eNB.Multiple E-RAB ID InstancesThe action failed because multiple instance of the same E-RAB had been provided to the eNB.Encryption and/or integrity protection algorithms not supportedThe eNB is unable to support any of the encryption and/or integrity protection algorithms supported by the UE.S1 Intra system Handover triggeredThe action is due to a S1 intra system handover that has been triggered.S1 Inter system Handover triggeredThe action is due to a S1 inter system handover that has been triggered.X2 Handover triggeredThe action is due to an X2 handover that has been triggered.Redirection towards 1xRTTThe release of the UE-associated logical S1 connection is requested due to redirection towards a 1xRTT system e.g., CS fallback to 1xRTT, or SRVCC to 1xRTT, when the PS service suspension is required in the EPC. During this procedure, the radio interface message might b