6.9 位置管理功能（含RAU和SRNS重选等信令流程）

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5)When resources for the transmission of user data between the target RNC and the new SGSN have been allocated and the new SGSN is ready for relocation of SRNS, the Forward Relocation Response message (Cause, RANAP Cause, and Target RNC Information) is sent from the new SGSN to the old SGSN. This message indicates that the target RNC is ready to receive from the source SRNC the forwarded downlink packets, i.e., the relocation resource allocation procedure is terminated successfully. RANAP Cause is information from the target RNC to be forwarded to the source SRNC. The RAB Setup Information, one information element for each RAB, contains the RNC Tunnel Endpoint Identifier and RNC IP address for data forwarding from the source SRNC to the target RNC. If the target RNC or the new SGSN failed to allocate resources, the RAB Setup Information element contains only NSAPI indicating that the source SRNC shall release the resources associated with the NSAPI. The Forward Relocation Response message is applicable only in case of inter-SGSN SRNS relocation.
   5）当在目标RNC和new SGSN之间为用户数据传输的资源都已经分配好了，并且new SGSN已经准备好了SRNS的重选，new SGSN发送转发重选响应消息（原因，RANAP原因，目标RNC信息）发送给old SGSN。这个消息指示目标RNC已经准备好接收从源SRNC过来的转发的下行PDU的接收。这就代表重选资源分配流程成功的完成了。RANAP原因是目标RNC将要转发给源SRNC的信息。RAB建立信息，是对每个RAB的一个信息元素，包含了从源SRNC到目标RNC的用于数据转发的RNC TEID和RNC IP地址。如果目标RNC或new SGSN分配资源失败，RAB建立信息元素将只包含NSAPI来指示源SRNC应释放和这个NSAPI关联的所有资源。转发重选响应消息仅在inter-SGSN SRNS重选的场景中可用。

6)   The old SGSN continues the relocation of SRNS by sending a Relocation Command (RABs to be released, and RABs subject to data forwarding) message to the source SRNC. The old SGSN decides the RABs subject to data forwarding based on QoS, and those RABs shall be contained in RABs subject to data forwarding. For each RAB subject to data forwarding, the information element shall contain RAB ID, Transport Layer Address, and Iu Transport Association. These are the same Transport Layer Address and Iu Transport Association that the target RNC had sent to new SGSN in Relocation Request Acknowledge message, and these are used for forwarding of downlink N‑DU from the source SRNC to the target RNC. The source SRNC is now ready to forward downlink data directly to the target RNC over the Iu interface. This forwarding is performed for downlink user data only.
   6)Old SGSN将继续SRNS的重选，发送重选命令消息（需要释放的RAB,需要数据前转的RAB)给源SRNC。old SGSN根据QOS决定需要数据前转的RAB，并且那些RAB应包含在“需要数据前转的RAB"字段里）。对于每一个“需要前转的RAB"字段，这个信息元素应包含RAB ID，传输层地址，Iu传输关联。这些传输层地址和Iu传输关联和目标RNC发送给new SGSN的重选请求确认消息中的一样，用于从源SRNC到目标RNC的下行N-PDU的转发。源SRNC现在已经准备好在Iu接口的到目标RNC的下行用户数据的直接转发。这个转发仅只针对下行用户数据。

7)The source SRNC may, according to the QoS profile, begin the forwarding of data for the RABs subject to data forwarding and starts the data-forwarding timer. The data forwarding at SRNS relocation shall be carried out through the Iu interface, meaning that the data exchanged between the source SRNC and the target RNC are duplicated in the source SRNC and routed at the IP layer towards the target RNC. For each radio bearer which uses lossless PDCP the GTP-PDUs related to transmitted but not yet acknowledged PDCP-PDUs are duplicated and routed at IP layer towards the target RNC together with their related downlink PDCP sequence numbers. The source RNC continues transmitting duplicates of downlink data and receiving uplink data.

   7)源SRNC可以，根据QOS Profile，开始为RAB转发需要前转的数据并且启动数据转发计时器。在SRNS重选中的数据转发应通过Iu接口执行，意味着在源SRNC和目标SRNC的数据交换将在源SRNC被复制，并且通过IP层发送给目标RNC。对于每个使用了无损PDCP的无线承载，已传输的相关的GTP-PDU但还没有被确认的PDCP-PDU，将被复制并和它们相关的下行PDCP序列号一起通过IP层路由传递到目标RNC。源RNC继续传送完全相同的下行数据和接收到的上行数据。

NOTE 2: The order of steps, starting from step 7 onwards, does not necessarily reflect the order of events. For instance, source RNC may send data forwarding (step 7) and start Relocation Commit message (step 8) almost simultaneously. Target RNC may send Relocation Detect message (step 9) and Cell Update Confirm/URA Update Confirm (or Cell Update Confirm/GRA Update Confirm) message (step 10) at the same time. Hence, target RNC may receive the UTRAN or GERAN Mobility Information Confirm message from MS (step 10) while data forwarding (step 8) is still underway, and before the new SGSN receives Update PDP Context Response message (step 11).
   Before the serving RNC role is not yet taken over by target RNC and when downlink user plane data starts to arrive to target RNC, the target RNC may buffer or discard arriving downlink GTP-PDUs according to the related QoS profile.
  注释2：步骤的顺序，从第7步开始往后，并不需要反映事件的顺序。例如，源RNC可以几乎同时发送数据转发（第7步）以及开始重选提交消息（第8步）。步骤9的目标RNC也可以同时发送重选检测消息和步骤10的小区更新确认/URA更新确认（或小区更新确认/GRA更新确认）消息。因此，目标RNC可以在步骤8的数据转发仍在路途中的时候接收第10步的UTRAN/GERAN移动性信息确认消息，并且是在第11步的new SGSN收到更新PDP上下文响应消息之前。

8)Before sending the Relocation Commit the uplink and downlink data transfer in the source, SRNC shall be suspended for RABs, which require delivery order.
  When the source SRNC is ready, the source SRNC shall trigger the execution of relocation of SRNS by sending a Relocation Commit message (SRNS Contexts) to the target RNC over the UTRAN Iur interface or over the GERAN Iur-g interface, respectively. The purpose of this procedure is to transfer SRNS contexts from the source RNC to the target RNC, and to move the SRNS role from the source RNC to the target RNC. SRNS contexts are sent for each concerned RAB and contain the sequence numbers of the GTP PDUs next to be transmitted in the uplink and downlink directions and the next PDCP sequence numbers that would have been used to send and receive data from the MS. . PDCP sequence numbers are only sent by the source RNC for radio bearers, which used lossless PDCP (see TS 25.323 [57]). The use of lossless PDCP is selected by the RNC when the radio bearer is set up or reconfigured. For PDP context(s) using delivery order not required (QoS profile), the sequence numbers of the GTP-PDUs next to be transmitted are not used by the target RNC.
  If delivery order is required (QoS profile), consecutive GTP-PDU sequence numbering shall be maintained throughout the lifetime of the PDP context(s). Therefore, during the entire SRNS relocation procedure for the PDP context(s) using delivery order required (QoS profile), the responsible GTP-U entities (RNCs and GGSN) shall assign consecutive GTP-PDU sequence numbers to user packets belonging to the same PDP context for uplink and downlink respectively.
   8)在发送重选提交之前，SRNC应为要求有序分发的RAB挂起源处的传输的上下行数据。
  当源SRNC准备好，源SRNC应通过在UTRAN的Iur接口或GERAN的Iur-g接口发送重选提交消息(SRNS上下文)给目标RNC来触发SRNS重选的执行。（Iur-g是为了让2G/3G更好通信，在BSC和RNC之间设立的一个接口）这个流程的目的是用于在源和目的RNC之间传递SRNS上下文。SRNS上下文将为每个有关联的RAB发送，并且包含了在上下行方向下一个将要传送的GTP PDU的序列号以及将要用于从MS发送和接收数据的下一个PDCP序列号。PDCP序列号仅由源RNC为无线承载来发送，使用无损PDCP(TS25.323)。无损PDCP的使用是由RNC在无线承载建立或重配置的时候来进行选择的。对于不要求有序分发的PDP上下文（QOS profile）,目标RNC将不使用下一个将被传输的GTP-PDU序列号。
  如果要求有序分发，连续的GTP-PDU序列号应在正在PDP上下文的生命周期内保持。因此，在为有按序分发要求的PDP上下文做的整个的SRNS重选流程中，负责GTP-U的实体（如RNC和GGSN)应给属于相同PDP上下文的上下行用户数据分配连续的GTP-PDU序列号。

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9)The target RNC shall send a Relocation Detect message to the new SGSN when the relocation execution trigger is received. For SRNS relocation type "UE not involved", the relocation execution trigger is the reception of the Relocation Commit message from the Iur interface. When the Relocation Detect message is sent, the target RNC shall start SRNC operation.
  9)目标RNC应发送重选检测消息给new SGSN---当收到重选执行触发的时候。对于SRNS重选类型为“UE不参与”，重选执行触发是从Iur接口收到的重选提交消息。当重选检测消息发送后，目标RNC应开始SRNC的操作。

10)The target SRNC sends a Cell Update Confirm / URA Update Confirm or Cell Update Confirm / GRA Update Confirm message. This message contains UE information elements and CN information elements. The UE information elements include among others new SRNC identity and S RNTI. The CN information elements contain among others Location Area Identification and Routeing Area Identification. The procedure shall be co-ordinated in all Iu signalling connections existing for the MS.
    10)目标SRNC发送一个小区更新确认/URA更新确认或小区更新确认/GRA更新确认消息。这个消息包含了UE信息元素和CN核心网信息元素。UE信息元素包含了新SRNC ID和S-RNTI等等。CN信息元素包含了LAI和RAI等等。这个流程应在这个MS存在的所有Iu信令连接上协调完成。
   Upon reception of the Cell Update Confirm / URA Update Confirm or Cell Update Confirm / GRA Update Confirm message the MS may start sending uplink user data to the target SRNC. When the MS has reconfigured itself, it sends the RAN Mobility Information Confirm message to the target SRNC. This indicates that the MS is also ready to receive downlink data from the target SRNC.
  一旦接收到小区更新确认/URA更新确认或小区更新确认/GRA更新确认消息，MS应开始发送上行用户数据给目标SRNC。当MS重新配置了它自己，它发送RAN移动性信息确认消息给目标SRNC。这将指示MS已经准备好从目标SRNC接收下行数据。
   If the new SGSN has already received the Update PDP Context Response message from the GGSN, it shall forward the uplink user data to the GGSN over this new GTP-U tunnel. Otherwise, the new SGSN shall forward the uplink user data to that GGSN IP address and TEID(s), which the new SGSN had received earlier by the Forward Relocation Request message.
  如果new SGSN已经从GGSN接收到Update PDP Context Response消息,它将通过新的GTP-U隧道将上行用户数据转发给GGSN。另外，new SGSN还应转发早些时候从转发重选请求消息里接收到的上行用户数据给这个GGSN IP地址和TEID。
   For using S4, if new the SGSN has already received the Modify Bearer Context Response message from the S GW, it shall forward the uplink user data to S GW over this new GTP U tunnel. Otherwise, the new SGSN shall forward the uplink user data to that S GW IP address and TEID(s), which the new SGSN had received earlier by the Forward Relocation Request message.
  对于使用S4接口的，如果new SGSN从SGW收到了Modify Bearer Response消息，它应通过新GTP-U隧道转发上行用户数据给SGW。另外，new SGSN还应转发早些时候从转发重选请求消息里接收到的上行用户数据给这个SGW IP地址和TEID。
   The target SRNC and the MS exchange the PDCP sequence numbers; PDCP SNU and PDCP SND. PDCP SND is the PDCP sequence number for the next expected in-sequence downlink packet to be received in the MS per radio bearer, which used lossless PDCP in the source RNC. PDCP SND confirms all mobile terminated packets successfully transferred before the SRNC relocation procedure. . If PDCP SND confirms the reception of packets that were forwarded from the source SRNC, the target SRNC shall discard these packets. PDCP SNU is the PDCP sequence number for the next expected in-sequence uplink packet to be received in the RNC per radio bearer, which used lossless PDCP in the source RNC. PDCP SNU confirms all mobile originated packets successfully transferred before the SRNC relocation. If PDCP SNU confirms reception of packets that were received in the source SRNC, the target SRNC shall discard these packets.
  目标SRNC和MS交换PDCP序列号DCP SNU和PDCP SND。PDCP SND是在每个无线承载上，MS预期接收的有序的下行数据的PDCP序列号，在源RNC中使用了无损PDCP。PDCP SND确认在SRNC重选流程之前，所有由手机接收的数据包被成功的传递。如果PDCP SND确认了从源SRNC转过来的数据包接收了，目标SRNC应丢弃这些包。PDCP SNU是在每个无线承载上，RNC预期接收的下一个按序上行链路数据包的PDCP序列号，在源RNC中使用了无损PDCP。PDCP SNU确认在SRNC重选之前所有由手机发起的数据包被成功的传递。如果PDCP SNU确认了在源SRNC中数据包的接收，目标SRNC应丢弃这些报文。

11) When the target SRNC receives the RAN Mobility Information Confirm message, i.e. the new SRNC ID + S RNTI are successfully exchanged with the MS by the radio protocols, the target SRNC shall initiate the Relocation Complete procedure by sending the Relocation Complete message to the new SGSN. The purpose of the Relocation Complete procedure is to indicate by the target SRNC the completion of the relocation of the SRNS to the CN.
   11)当目标SRNC接收到了RAN移动性信息确认消息，也就是new SRNC-ID +S-RNTI通过空口协议和MS成功的交换，目标SRNC应发起重选完成流程---通过发送一个重选完成消息给new SGSN。重选完成流程的目的是由目标SRNC来指示SRNS到CN的重选的完成。

12) Upon receipt of Relocation Complete message, if the SRNS Relocation is an inter SGSN SRNS relocation, the new SGSN signals to the old SGSN the completion of the SRNS relocation procedure by sending a Forward Relocation Complete message.
  12)一旦接收到重选完成消息,如果SRNS重选是一个inter-SGSN SRNS重选，new SGSN告知old SGSN关于SRNS重选流程的完成---通过发送转发重选完成消息。

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13) Upon receipt of the Relocation Complete message, the CN shall switch the user plane from the source RNC to the target SRNC. If the SRNS Relocation is an inter-SGSN SRNS relocation or if Direct Tunnel was established in intra-SGSN SRNS relocation, the new SGSN sends Update PDP Context Request messages (new SGSN Address, SGSN Tunnel Endpoint Identifier, QoS Negotiated, Negotiated Evolved ARP, serving network identity, CGI/SAI, RAT type, MS Info Change Reporting support indication, NRSN, DTI) to the GGSNs concerned. The SGSN shall send the serving network identity to the GGSN. If Direct Tunnel is established the SGSN provides to GGSN the RNC's Address for User Plane and TEID for Downlink data and shall include the DTI to instruct the GGSN to apply Direct Tunnel specific error handling procedure as described in clause 13.8. NRSN indicates SGSN support of the network requested bearer control. The inclusion of the Negotiated Evolved ARP IE indicates that the SGSN supports the Evolved ARP feature. If the new SGSN did not receive a Negotiated Evolved ARP IE in the SGSN Forward Relocation Request message from the old SGSN then the new SGSN shall derive this value from the Allocation/Retention Priority of the QoS profile negotiated according to Annex E of TS 23.401 [89]. The GGSNs update their PDP context fields and return an Update PDP Context Response (GGSN Tunnel Endpoint Identifier, Prohibit Payload Compression, APN Restriction, MS Info Change Reporting Action, CSG Information Reporting Action, BCM, Negotiated Evolved ARP) message. The GGSN sets the Negotiated Evolved ARP based on local policy or PCC. The Allocation/Retention Priority of the QoS Profile Negotiated is derived from the Evolved ARP according to the mapping principles of TS 23.401 [89], Annex E. The Prohibit Payload Compression indicates that the SGSN should negotiate no data compression for this PDP context. The SGSN shall apply the Negotiated Evolved ARP if received from the GGSN.
   13)一旦接收到重选完成消息，CN应将用户平面从源RNC切换到目标SRNC。如果SRNS重选是一个inter-SGSN SRNS重选或如果直接隧道在一个intra-SGSN SRNS重选流程中建立，new SGSN发送Update PDP Context Request 消息（新SGSN地址,SGSN TEID,协商的QOS，演进的协商ARP，服务网络ID，CGI/SAI，RAT类型，MS信息变化报告支持指示，NRSN,DTI)给关联的GGSN.SGSN应发送服务网络ID给GGSN.如果直接隧道建立，SGSN给GGSN提供RNC的用户平面地址和下行数据的TEID，并且应包含DTI（direct tunnel ID)来指示GGSN要应用直接隧道，指定的错误处理流程在13.8描述。NRSN指示GGSN关于网络请求的承载控制能力的支持。协商的演进ARP IE指示SGSN支持演进的ARP特性。如果new SGSN没有从old SGSN的SGSN转发重选请求消息里看到演进协商ARP IE，那么new SGSN应根据TS23.401的附录E里描述的那样，从QOS profile里的分配/保持优先级里去获取这个值。GGSN更新它的PDP上下文字段并且返回一个更新PDP上下文响应（GGSN TEID,禁止payload压缩、APN限制、MS信息变化报告行动、CSG信息报告心动、BCM、协商的演进ARP）消息。GGSN根据本地策略或PCC来设置演进的协商的ARP。协商的QOS profile里包含的分配/保持优先级是从演进的ARP根据TS23.401附录E的映射原则映射过来的。禁止payload压缩指示SGSN应为这个PDP上下文协商无数据压缩。SGSN如果从GGSN收到，则应用用这个协商的演进ARP值。

14) Upon receiving the Relocation Complete message or if it is an inter-SGSN SRNS relocation, the Forward Relocation Complete message, the old SGSN sends an Iu Release Command message to the source RNC. When the RNC data-forwarding timer has expired the source RNC responds with an Iu Release Complete.
An old S4-SGSN starts a timer to supervise when resources in old Serving GW (in case of Serving GW change or in case of S4 to Gn/Gp SGSN change) shall be released. When this timer expires the old S4-SGSN releases the S GW resources. The old S4-SGSN deletes S-GW bearer resources by sending Delete Session Request (Cause, Operation Indication) messages to the SGW. If ISR is activated the Cause indicates that the old S-GW shall delete the bearer resources on the other old CN node by sending Delete Bearer Request message to the other CN node. The Operation Indication flag is not set by the old S4-SGSN. This indicates to the S-GW that the S GW shall not initiate a delete procedure towards the PDN GW.
   14)一旦接收到重选完成消息或这是一个inter-SGSN SRNS重选；转发重选完成消息, old SGSN发送一个Iu释放命令消息给源RNC。当RNC数据转发计时器超时，源RNC响应一个Iu释放完成消息。

   一个old S4-SGSN开启计时器来监管在old SGW的资源什么时候应该释放（在SGW变化或S4到Gn/Gp SGSN变化的场景）。当这个计时器超时，old S4-SGSN释放SGW的资源。old S4-SGSN发送delete session request（原因，操作指示）消息个SGW来删除SGW承载资源。如果ISR激活，原因指示old SGW应通过发送delete bearer request消息给其他CN节点来删除这些old CN节点的承载资源。操作指示flag不由old S4-SGSN设置。这个flag指示SGW，SGW不应发起到PGW的delete流程。

15) After the MS has finished the Cell / URA update or the Cell / GRA update and RNTI reallocation procedure and if the new Routeing Area Identification is different from the old one, the MS initiates the Routeing Area Update procedure. See clause "Location Management Procedures (Iu mode)". Note that it is only a subset of the RA update procedure that is performed, since the MS is in PMM CONNECTED state.

      The new SGSN shall determine the Maximum APN restriction based on the received APN Restriction of each PDP context/EPS Bearer context for using S4 from the GGSN/P‑GW or old S4-SGSN for using S4 and then store the new Maximum APN restriction value.

     If Routeing Area Update occurs, the SGSN shall determine whether Direct Tunnel can be used based on the received GPRS CAMEL Subscription Information. If Direct Tunnel can not be maintained the SGSN shall re-establish RABs and initiate the Update PDP Context procedure to update the IP Address and TEID for Uplink and Downlink data.

  15)在MS完成了小区/URA更新或小区/GRA更新以及RNTI重选流程并且如果新的RAI和之前老的不同的话，MS发起RAU流程。注意这里是RAU流程的一个子集（即一部分流程）将执行，因为MS已经是PMM-CONNECTED状态。

  New SGSN应根据使用S4的GGSN/PGW或old S4-SGSN收到的每个PDP上下文/EPS承载上下文的APN限制，来决定最大的APN限制，并存储为新的最大APN限制值。

  如果RAU发生，SGSN应决定直接隧道功能是否能根据收到的GPRS CAMEL签约信息来使用。如果直接隧道不能保持，SGSN应重新建立RAB并且发送update PDP context流程来更新上下行数据的IP地址和TEID。

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  The purpose of the SRNS Relocation Cancel procedure is to cancel an ongoing SRNS relocation. The SRNS Relocation Cancel procedure may be initiated during or after the Relocation Preparation procedure and may be initiated by the source RNC.  
  SRNS重选取消流程的目的是取消一个正在进行的SRNS重选.SRNS重选取消流程可以在重选准备流程期间或者之后发起，并可以是由源RNC发起。

   The SRNS Relocation Cancel procedure is illustrated in Figure 44. The sequence is valid for cancelling both an intra-SGSN SRNS relocation and an inter-SGSN SRNS relocation.
    SRNS重选取消流程在图例44描述.对于intra-SGSN还是inter-SGSN的SRNS重选的取消，顺序都是适用的。

Figure 44: SRNS Cancel Relocation Procedure

NOTE: All steps in figure 44, except steps (A), are common for architecture variants using Gn/Gp based SGSN and using S4 based interaction with S GW. For an S4 based interaction with S GW, procedure steps (A) are defined in the clause 6.9.2.2.4a.

   注释：图例44中的所有步骤,除了步骤A,对于采用基于Gn/Gp的SGSN或基于S4的SGW，都是公共的架构。对于基于S4接口的，与SGW的交互，流程步骤A在章节6.9.2.2.4a定义。

1) An SRNS Relocation procedure has started, as specified in clause 6.9.2.2.1.
   1)个SRNS重选流程发起了，就像6.9.2.2.1描述的那样.

2a) The SRNS Cancel Relocation may be initiated by a timer expiry or by an error event in the source RNC.
    2a)SRNS取消重选可以由源RNC的一个计时器超时或一个错误事件触发.

2b) When one of conditions in 2a is satisfied, the source RNC sends a Relocation Cancel (Cause) to the old SGSN. Cause indicates the reason for cancelling the ongoing SRNS relocation.
    2b)当2a中的一个条件满足的时候,源RNC发送一个重选取消（原因）给old SGSN.原因指示了取消这个正在进行的SRNS重选的原因。

3) The old SGSN sends a Relocation Cancel Request (RANAP Cause) to the new SGSN to indicate that the ongoing SRNS relocation should be cancelled. RANAP Cause contains the cause value received by the source RNC in the Relocation Cancel message.
     3)old SGSN发送一个重选取消请求（RANAP原因）给new SGSN来指示这个进行中的SRNS重选应该被取消.RANAP原因包含了从源RNC的重选取消消息中包含的原因值。

4) The new SGSN sends an Iu Release Command (Cause) to request from the target RNC to release the Iu resources already allocated for the SRNS relocation, or to cancel the ongoing allocation of Iu resources for the SRNS relocation. Cause is set equal to RANAP Cause, i.e. to whatever cause value was included in the Relocation Cancel Request received from old SGSN. The target RNC releases the requested Iu resources and responds with an Iu Release Complete.
    4)new SGSN发送一个Iu release命令（原因）来请求目标RNC来释放已经分配给这个SRNS重选的资源,或取消为这个SRNS重选分配的Iu资源.原因和值和RANAP原因值相等，即任何时候这个原因值包含在从old SGSN收到的重选取消请求消息中。目标RNC释放请求的Iu资源并响应一个Iu release 完成消息。

5) The new SGSN acknowledges the cancellation of the ongoing SRNS Relocation by sending a Relocation Cancel Response to the old SGSN.
    5)new SGSN发送重选取消响应给old SGSN来确认取消SRNS的重选.

6) The old SGSN responds to the source RNC with a Relocation Cancel Ack message.

     6)old SGSN响应一个重选取消确认消息给源RNC。

爱卫生

    The procedures described in figures 44a shows only the steps (A)  due to use of S4, which are different from the Gn/Gp variant of the procedure given by clauses 6.9.2.2.4.                                                                           

    在图例44a中描述了仅因为S4接口的使用而产生的A步骤,和6.9.2.2.4描述的基于Gn/Gp接口的流程稍有不同。

                                                               Figure 44a1: A) for SRNS Relocation Cancel Procedure Using S4
A1. This step is only performed in case of handover from S4-SGSN to S4-SGSN with Serving GW relocation or handover from Gn/Gp SGSN to S4-SGSN. The New S4-SGSN deletes the EPS bearer resources by sending Delete Session Request (Cause) messages to the New S GW.
A2. The New S GW acknowledges with Delete Session Response messages.

    A1.这个步骤只在从S4-SGSN到带有SGW重选的S4-SGSN切换，或从Gn/Gp SGSN到S4-SGSN的切换时执行.新S4-SGSN删除EPS承载资源---通过发送delete session request（原因）消息给新的SGW。

    A2.新SGW发送一个delete session response消息进行确认。

爱卫生

The procedure can be used for relocation when source SRNC and target RNC are connected to same SGSN.
   这个流程可以用于当源SRNC和目标RNC连接到相同的SGSN的时候使用。
NOTE 1: If the MS is both MM-CONNECTED and PMM-CONNECTED, then this procedure can only be used if the source RNC and target RNC are connected to same MSC.
  注释1：如果MS是在MM-CONNECTED和PMM-CONNECTED状态,那这个流程仅当源和目的RNC连接到相同的MSC的时候使用。
This procedure is only performed for an MS in PMM CONNECTED state where the Iur interface is available between a serving RNC and a drifting RNC. This procedure is not applicable for GERAN.
   这个流程仅当MS在PMM-CONNECTED状态的时候，并且在服务RNC和漂移RNC之间存在Iur接口的时候采用。这个流程不适用于GERAN。
In Enhanced Serving RNS Relocation the SRNS functionality is prepared at RAN side and the SGSN is not informed until the preparation and execution of the relocation has taken place, the preparation and execution phases are performed as specified in TS 25.423 [95]. The completion phase is illustrated in Figure 44a below.
    在增强的服务RNS重选时,SRNS功能由RAN侧来准备并且SGSN没有被通知---直到重选的准备和执行发生，准备和执行阶段的执行由TS25.423描述.完成阶段由图例44a2描述。

Figure 44a2: Enhanced Serving RNS Relocation

NOTE 2: The figure shows the user plane connections when Direct Tunnel is established. If Direct Tunnel is not established only the user plane between RNC and SGSN is impacted due relocation.

   注释2：图例显示了当直接隧道建立的时候的用户面连接.如果直接隧道没有建立,则只有RNC和SGSN之间的用户平面在重选期间会受到影响。
There are three phases for the Enhanced Serving RNS Relocation.
Preparation Phase:
- The Source RNC decides to relocate the UE to a neighbouring RNC (Target RNC).
- The Source RNC triggers the RNSAP: Enhanced Relocation procedure.
Execution Phase:
- The RNC triggers the relocation to MS.
- The Source RNC may start data forwarding.

   有3个阶段用于增强的服务RNS重选.

准备阶段：

- 源RNC决定重选UE到一个邻居的RNC（目标RNC)。

- 源RNC触发RNSAP:增强的重选流程。

执行阶段：

- RNC触发到MS的重选.

- 源RNC可以开始数据转发.

Completion Phase:完成阶段：
1. The MS has been relocated to the Target RNC.

   1.MS已经重选到目标RNC.
2. The Target RNC sends Enhanced Relocation Complete Request message to the SGSN to indicate that the MS was relocated to the Target RNC. The Target RNC indicates successfully relocated, modified or released RABs to the SGSN.

    2.目标RNC发送增强重选完成请求消息给SGSN来指示,MS已经重选到目标RNC.目标RNC向SGSN发送成功重选、修改或释放的RAB的指示。
3. Upon receipt of the enhanced Relocation Complete message, the SGSN shall switch the user plane from the source RNC to the target SRNC. If Direct Tunnel was established, the SGSN sends Update PDP Context Request messages (SGSN Address, SGSN Tunnel Endpoint Identifier, QoS Negotiated, Negotiated Evolved ARP, serving network identity, CGI/SAI, RAT type, MS Info Change Reporting support indication, NRSN, DTI) to the GGSNs concerned. The SGSN shall send the serving network identity to the GGSN. If Direct Tunnel is established the SGSN provides to GGSN the RNC's Address for User Plane and TEID for Downlink data and shall include the DTI to instruct the GGSN to apply Direct Tunnel specific error handling procedure as described in clause 13.8. NRSN indicates SGSN support of the network requested bearer control. The GGSNs update their PDP context fields and return an Update PDP Context Response (GGSN Tunnel Endpoint Identifier, Prohibit Payload Compression, APN Restriction, MS Info Change Reporting Action, CSG Information Reporting Action, BCM, Negotiated Evolved ARP) message. The GGSN sets the Negotiated Evolved ARP based on local policy or PCC. The Allocation/Retention Priority of the QoS Profile Negotiated is derived from the Evolved ARP according to the mapping principles of TS 23.401 [89], Annex E. The Prohibit Payload Compression indicates that the SGSN should negotiate no data compression for this PDP context. The SGSN shall apply the Negotiated Evolved ARP if received from the GGSN.
    For an S4 based interaction with S GW and P GW procedure step (A) is defined in clause 6.9.2.2.5A.

   3.一旦接收到增强重选完成消息,SGSN应将用户平面从源RNC切换到目标SRNC.如果直接隧道建立，SGSN发送update pdp context request消息（SGSN地址、SGSN TEID、协商的QOS、协商的演进ARP、服务网络ID、CGI/SAI、RAT类型、MS信息变化报告支持指示、NRSN、DTI)给关联的GGSN。SGSN应发送服务网络ID给GGSN。如果直接隧道建立，SGSN给GGSN提供RNC的用户平面地址和下行数据的TEID，并且应包含DTI（direct tunnel ID)来指示GGSN要应用直接隧道，指定的错误处理流程在13.8描述。NRSN指示GGSN关于网络请求的承载控制能力的支持。GGSN更新它的PDP上下文字段并且返回一个update pdp context response消息.GGSN根据本地策略或PCC设置协商的演进ARP IE。协商的QOS profile中的分配/保持优先级是从演进的ARP根据TS23.401的附录E提到的映射原则，映射过来的.禁止payload压缩指示SGSN应为这个PDP上下文协商无数据压缩。SGSN如果从GGSN收到了,则应应用这个协商的演进ARP。

4. The SGSN configures the necessary Iu resources for the Target RNC and responds with Enhanced Relocation Complete Response.
   4.SGSN为目标RNC配置必要的Iu资源,并响应一个增强重选完成响应消息。

5. After sending the Enhanced Relocation Complete Response message to the Target RNC the SGSN sends an Iu Release Command message to the source RNC and the source RNC responds with an Iu Release Complete.
    5.在发送增强重选完成响应消息给目标RNC之后,SGSN发送一个Iu release command消息给源RNC，源RNC响应一个Iu release complete消息。

6. If the Routeing Area Identification is different from the old one the MS initiates the Routeing Update procedure. See clause 6.9.2. Like after the relocation procedures described in clauses above e.g. clause 6.9.2.2.1, only a subset of the RA update is performed, since the MS is in PMM-CONNECTED state.

    6.如果RAU和之前老的不同,MS发起RAU流程.参见6.9.2.同样，这里只执行一个RAU流程的子集，因为MS已经是PMM-CONNECTED状态。

爱卫生

Two procedures are defined depending on whether the Serving GW is unchanged or relocated, figures 44b and 44c show only the steps 3 and 4 due to use of S4, which is different from the Gn/Gp variant defined in clause 6.9.2.2.5.
A1) Procedure using S4 without Serving GW relocation
   根据SGW是否改变或重选,图例44b和44c显示了使用S4接口时，只有步骤3和4不同的两个流程,和6.9.2.2.5描述的基于Gn/Gp接口的流程稍有不同。
A1) 使用S4但不发生SGW重选的流程:

Figure 44b1: Step 3 for Enhanced Serving RNS Relocation without Serving GW relocation using S4

NOTE 1: Steps A) and B) are common for architecture variants with GTP based S5/S8 and PMIP-based S5/S8.
   注释1：步骤A和B对于使用GTP或PMIP的S5/S8接口来说是公共的。

A) If Direct Tunnel was established the SGSN update these EPS Bearer contexts by sending Modify Bearer Request (SGSN Tunnel Endpoint Identifier for Control Plane, EPS Bearer ID(s), SGSN Address for Control Plane, SGSN Address(es) and TEID(s) (if Direct Tunnel is not used) or RNC Address(es) and TEID(s) for User Traffic (if Direct Tunnel is used), PDN GW addresses and TEIDs (for GTP based S5/S8) or GRE keys (for PMIP based S5/S8) at the PDN GW(s) for uplink traffic, serving network identity, CGI/SAI, RAT type, MS Info Change Reporting support indication, DTI). If Direct Tunnel is established the SGSN shall include the DTI to instruct the S GW to apply Direct Tunnel specific error handling procedure as described in clause 13.8. The SGSN puts the according NSAPI in the field of EPS Bearer ID.
  A)如果直接隧道建立,SGSN发送发送修改承载请求消息（SGSN控制平面TEID,EPS承载ID,SGSN控制平面地址,SGSN地址和TEID（如果直接隧道没有使用）或RNC的用户平面地址和TEID(如果直接隧道使用了的话）,PGW上的上行流量的PGW地址和TEID(基于GTP的S5/S8)或GRE key（基于PMIP的S5/S8),服务网络ID,CGI/SAI,RAT类型,MS信息变更报告支持指示,DTI）来更新这些EPS Bearer上下文。如果直接隧道建立了,SGSN应包含DTI来指示SGW来应用直接隧道,相关错误处理流程在章节13.8定义。SGSN将相应的NSAPI放到EPS承载ID字段中。

B) If MS Info Change Reporting is started, the S GW sends Modify Bearer Request (EPS Bearer ID(s), serving network identity, CGI/SAI, RAT type, MS Info Change Reporting support indication) messages to the P GWs involved.
  B)如果MS信息变化报告启动了,SGW发送modify bearer request（EPS Bearer ID,服务网络ID,CGI/SAI,RAT类型,MS信息变更报告支持指示）消息给相应的PGW.

C) The P GWs acknowledge with sending Modify Bearer Response (TEID, Prohibit Payload Compression, MS Info Change Reporting Action, CSG Information Reporting Action) messages to S GW. The Prohibit Payload Compression indicates that the SGSN should negotiate no data compression for this EPS Bearer context.
   C)PGW响应一个modify bearer response(TEID,禁止payload压缩,MS信息变更报告行动,CSG信息报告心动)消息给SGW。禁止payload压缩指示SGSN应为这个EPS Bearer上下文协商无数据压缩。

D) The Serving GW acknowledges the user plane switch to the SGSN via the message Modify Bearer Response (Cause, Serving GW Tunnel Endpoint Identifier for Control Plane, Serving GW Address for Control Plane, Protocol Configuration Options, PDN GW addresses and TEIDs (for GTP based S5/S8) or GRE keys (for PMIP based S5/S8) at the PDN GW(s) for uplink traffic, Prohibit Payload Compression, MS Info Change Reporting Action, CSG Information Reporting Action). At this stage the user plane path is established for all EPS Bearer contexts between the UE, target RNC, SGSN in case Direct Tunnel is not used, Serving GW and PDN GW.
  D)SGW通过modify bearer response（原因、SGW控制面TEID、SGW控制面地址、PCO、PGW上的用于上行流量的PDW地址和TEID(针对基于GTP的S5/S8)或GRE密钥（针对基于PMIP的S5/S8)、禁止payload压缩、MS信息变化报告行动、CSG信息报告行动）消息来确认用户平面切换到SGSN.在这个阶段，所有EPS承载上下文的用户面路径已经在UE、目标RNC、SGSN（如果没用直接隧道），SGW和PGW之间建立。

A2) Procedure using S4 with Serving GW relocation and Direct Tunnel
This procedure is used if the SGSN determines the Serving Gateway is to be relocated.   A2)基于S4接口并且发生了SGW重选和直接隧道的流程   这个流程在当SGSN决定SGW需要发生重选的时候使用。

Figure 44b2: Step 3 for Enhanced Serving RNS Relocation without Serving GW relocation using S4

NOTE 2: Steps A) and B) are common for architecture variants with GTP based S5/S8 and PMIP-based S5/S8.
   注释2：步骤A和B对于基于GTP和PMIP的S5/S8接口来说是公共的架构。  

A) The SGSN selects the new Serving GW as described in TS 23.401 [89] under clause 4.3.8.2 on "Serving GW selection function", and sends a Create Session Request message (SGSN Tunnel Endpoint Identifier for Control Plane, EPS Bearer ID(s), SGSN Address for Control Plane, SGSN Address(es) and TEID(s) (if Direct Tunnel is not used) or RNC Address(es) and TEID(s) for User Traffic (if Direct Tunnel is used), PDN GW addresses and TEIDs (for GTP based S5/S8) or GRE keys (for PMIP based S5/S8) at the PDN GW(s) for uplink traffic, serving network identity, CGI/SAI, RAT type, MS Info Change Reporting support indication, DTI). If Direct Tunnel is established the SGSN shall include the DTI to instruct the S GW to apply Direct Tunnel specific error handling procedure as described in clause 13.8.
   A) SGSN根据TS23.401章节4.3.8.2的描述来选择一个新的SGW,并发送一个create session request消息(SGSN控制面TEID,EPS承载ID,SGSN控制面地址、SGSN地址和TEID(如果直接隧道未使用）或RNC用户面的地址和TEID（如果直接隧道使用）,PGW上用于上行流量的PGW地址和TEID(基于GTP的S5/S8)或GRE密钥（基于PMIP的S5/S8），服务网络ID,CGI/SAI,RAT类型,MS信息变更报告支持指示,DTI)。如果直接隧道建立，SGSN应包含DTI来指示SGW来应用直接隧道,相关错误处理流程在章节13.8定义。

B) The new SGW sends Modify Bearer Request (EPS Bearer ID(s), serving network identity, CGI/SAI, RAT type, MS Info Change Reporting support indication) messages to the P GWs involved.
   B)新SGW发送modify bearer request(EPS承载ID,服务网络ID,CGI/SAI,RAT类型,MS信息变化报告支持指示）消息给PGW。

C) The P GWs acknowledge with sending Modify Bearer Response (TEID, Prohibit Payload Compression, MS Info Change Reporting Action, CSG Information Reporting Action) messages to new S GW. The Prohibit Payload Compression indicates that the SGSN should negotiate no data compression for this EPS Bearer context.
   C) PGW发送modify bearer response(TEID,禁止payload压缩,MS信息变化报告行动、CSG信息报告行动）消息给新SGW进行确认。禁止payload压缩指示SGSN应为这个EPS承载上下文协商无数据压缩。

D) The new Serving GW acknowledges the user plane switch to the SGSN via the message Create Session Response (Cause, Serving GW Tunnel Endpoint Identifier for Control Plane, Serving GW Address for Control Plane, Protocol Configuration Options, PDN GW addresses and TEIDs (for GTP based S5/S8) or GRE keys (for PMIP based S5/S8) at the PDN GW(s) for uplink traffic, Prohibit Payload Compression, MS Info Change Reporting Action, CSG Information Reporting Action). The SGSN starts timer, to be used in step F.
     D)新SGW通过create session response（原因、SGW控制面TEID、SGW控制面地址、PCO、PGW上的用于上行流量的PDW地址和TEID(针对基于GTP的S5/S8)或GRE密钥（针对基于PMIP的S5/S8)、禁止payload压缩、MS信息变化报告行动、CSG信息报告行动）消息来确认用户平面切换到SGSN.SGSN启动一个计时器，将在步骤F中用到。
E) The SGSN configures the necessary Iu resources for the Target RNC and responds with Enhanced Relocation Complete Response. The SGSN provides to the target RNC the new S GW's Address for user Plane and TEID(s) for Uplink data. The target RNC starts using the new Serving GW address and TEID(s) for forwarding subsequent uplink packets.
    E)SGSN为目标RNC配置必要的Iu资源并响应一个增强的重选完成响应。SGSN给目标RNC提供new SGW的用于上行数据的用户面地址和TEID。目标RNC开始使用new SGW的地址和TEID来用于转发后续的上行数据。

F) When the timer has expired after step D, the SGSN releases the bearer(s) in old S GW by sending a Delete Session Request message.
    F)当在步骤D中描述的计时器超时,SGSN发送delete session request消息给old SGW要求释放承载。

G) The old SGW acknowledge bearer deletion.

    G)old SGW确认承载的删除。

爱卫生

All GPRS-attached MSs, except A/Gb mode MSs in class B mode of operation engaged in CS communication, shall perform periodic RA updates. MSs that are IMSI-attached and not GPRS-attached shall perform periodic LA updates. Periodic RA updates are equivalent to intra SGSN routeing area updates as described in clause "Intra SGSN Routeing Area Update", with Update Type indicating periodic RA update. For MSs that are both IMSI-attached and GPRS-attached, the periodic updates depend on the mode of operation of the network:
   所有GPRS附着的MS,除了A/Gb模式的B类手机正在参与CS的通信外,都应执行周期性的RA更新流程。IMSI附着并且非GPRS附着的MS应执行周期性的LA更新。周期性的RAU和intra SGSN RAU是等价的---在章节“Intra SGSN Routeing Area Update"中描述，并且设置更新类型为周期性RA更新。对于MS同时IMSI附着和GPRS附着,周期性的RA更新取决于网络的模式：
- If the network operates in mode I, periodic RA updates shall be performed, and periodic LA updates shall not be performed. In this case, the MSC/VLR shall disable implicit detach for GPRS-attached MSs and instead rely on the SGSN to receive periodic RA updates. If periodic RA updates are not received in the SGSN and the SGSN detaches the MS, the SGSN shall notify the MSC/VLR by sending an IMSI Detach Indication message.
-如果是网络模式I,周期性RAU应执行,并且周期性LAU不应执行.在这种情况下,MSC/VLR应禁止GPRS附着的MS的隐式去附着，并且作为替代的，依赖于SGSN来接收周期性RAU。如果周期性RAU没有从SGSN收到并且SGSN去附着了这个MS，SGSN应发送IMSI detach indication消息来通知MSC/VLR。
- If the network operates in mode II or mode III, both periodic RA updates and periodic LA updates shall be performed independently. RA updates are performed towards the SGSN, and LA updates are performed towards the MSC/VLR.
-如果网络工作在模式II或模式III,无论周期性RAU和周期性LAU都应同时执行.RAU的执行朝向SGSN,LAU的执行朝向MSC/VLR.
In A/Gb mode, the periodic RA update timer in the MS is stopped when an LLC PDU is sent since all sent LLC PDUs set the MM context state to READY. The periodic RA update timer is reset and started when the state returns to STANDBY.
   在A/Gb模式,在一个LLC PDU发送的时候，MS中的周期性RAU计时器停止，因为所有发送的LLC PDU将MM上下文状态设置为READY.周期性RAU计时器将在状态返回到STANDBY的时候重置并启动。
In Iu mode, the periodic RA update timer in the MS is stopped when the MM context enters the PMM CONNECTED state. The periodic RA update timer is reset and started when the state returns to PMM IDLE state.
    在Iu模式,当MM上下文进入到PMM-CONNECTED状态的时候，MS中的周期性RAU计时器停止.当状态返回到PMM-IDLE的时候，周期性的RAU计时器将重置并启动。
If the MS could not successfully complete the periodic RA update procedure after a retry scheme while the MS was in GERAN/UTRAN PS coverage, the MS shall wait a back-off time equal to the periodic LA update timer broadcast by the network before restarting the periodic RA update procedure.
NOTE:If ISR is activated, additional handling in MS and SGSN is described in TS 23.401 [89].
     如果一个在GERAN/UTRAN的PS覆盖范围的MS，不能成功的完成周期性RAU流程，并且尝试了重选机制后仍不行，MS应在重启RAU流程之前等待一个后退时间（等于网络侧广播的周期性LAU计时器).
     注释：如果ISR激活,额外的处理请参考TS23.401.

爱卫生

The PS Handover procedure is used to handover an MS with one or more packet flows from a source cell to a target cell, when at least one of the cells is a GERAN cell. The source and target cells can be located within either the same BSS (Intra BSS HO), different BSSs within the same SGSN (Intra SGSN HO) or belonging to different SGSNs (Inter SGSN HO), or systems with different radio access types (Inter RAT HO, Inter mode HO).
   PS切换流程用于将一个带有一个或多个数据包流的MS从一个源小区切换到目标小区,并且这些小区至少有一个是GERAN(GPRS Edge Radio Access Network)小区.源和目标小区的位置可以处在同一个BSS下（Intra BSS切换),或相同SGSN的不同BSS（Intra SGSN切换）或属于不同SGSN（Inter-SGSN切换），或不同无线接入技术系统之间的切换（Inter-RAT切换）.
While the MS is still in the source cell:
- Radio resources in the target cell are allocated and signalled to the MS.
- System information of the target cell needed for access in the target cell is signalled to the MS.
After handover between GERAN and UTRAN is complete, the RAU procedure is performed even if the RAI has not changed.
The complete PS Handover procedures are defined in TS 43.129 [87].
The complete Inter RAT HO between E UTRAN and GERAN procedures are defined in TS 23.401 [89].
   当MS仍在源小区：
- 目标小区的无线资源已经为MS分配并且告知MS。
- 需要在目标小区接入的目标小区的系统信息也告知了MS。
  在完成GERAN到UTRAN的切换后，RAU流程将要执行---即使RAI没有发生变化。
  完整的PS切换流程在TS43.129定义。
  完整的在E-UTRAN和GERAN的Inter-RAT切换在TS23.401定义。

爱卫生

   此部分只有一页的简要描述，而且在国内现网里没有。因此本部分跳过。
   TOM(tunnelling of message) 的主要作用是可以将一些非GSM的信令消息通过TOM协议将消息发给SGSN，再由SGSN通过Gs接口并使用BSSAP+协议透传给非GSM的MSC/VLR。例如CDMA网络中的或固网中的类似节点。

Albert

不知版主是按哪个版本翻译的，是R7么？貌似比R7多了不少东东！

爱卫生

回复 Albert 的帖子

   在首页的版块描述里提到了。是R10.2.0版本。(日期为2010年12月)。你说得对，大的变化是从R8开始的，因为在R8架构里引入了EPC（演进的包交换核心网）也就是在LTE无线接入技术下对应的核心网的演进架构（所以有些文档也叫SAE)。因此在TS23.060里也做了一些更新，主要是增加了S3和S4接口用于2G/3G的PS核心网和LTE的核心网EPC进行的互操作，例如切换等。
   有一个术语需要了解，在规范中提到如果是S4-SGSN，实际上就是指的R8版本之后的SGSN，因为它支持S4接口（是SGSN到EPC的SAE GW的接口)。如果是R8之前的SGSN，在规范或别的文档中，一般有一个术语称呼它为Gn-SGSN。
   你看得很仔细啊！呵呵！{:soso_e100:}

Albert

呵呵，多谢。正好不知道S4-SGSN呢这个术语什么意思。版主就给回答了。我目前看的是R7版本。也不是仔细了，主要是理论的东东还是得扎实掌握一下。{:soso_e100:}

cmcc_demon

其实很想把规范的翻译作为自己日常坚持的一项工作，自己翻译去理解的会更加深刻！哎，你们太勤奋了，有点坐享其成的感觉！

爱卫生

回复 cmcc_demon 的帖子

   没有啦。其实我也很懒的。我还给自己颁了一枚“懒”勋章。我只是偶尔有点激情而已。呵呵。不过如果所处的整体学习氛围、交流气氛好的话，我是很容易受到感染的。
   demon兄，你已经很勤奋啦。不要太谦虚。

mobileice

楼主辛苦了，写的好多呀

samsin

谢谢爱版主，东西搞的太细了，
请教个问题： inter-sgsn RAU里面，23060里面在描述sgsn context 消息的时候，当old sgsn 向new sgsn传用户数据的时候 用到的一个N-PDU，我认为这里应该是T-PDU更合适，为什么 协议里要用N-PDU这个 词呢，按理说N-PDU应该是在gb口，传输用户数据时候提到的东东，而这里是GN口，准确的说是被gtp-u 承载的T-PDU啊！再说应该是老sgsn把用户的残留数据通过新的sgsn发给用户，那么新的sgsn在发给用户的时候，用SNDCP分段等啥的，这个时候才会提到 N-PDU啊！
请爱版主，指点下

爱卫生

samsin 发表于 2011-10-4 20:06
谢谢爱版主，东西搞的太细了，
请教个问题： inter-sgsn RAU里面，23060里面在描述sgsn context 消息的时候 ...

  谈不上指点。我只能说下我的看法，也不一定对的。至于使用N-PDU和T-PDU，我个人还是偏向N-PDU。正如你所说，N-PDU其实是用户的Payload已经到达SGSN，在SNDCP层缓存后，准备交给LLC层传递之前的数据。看TS44065的原文是这样：“The N-PDUs shall be buffered in the SNDCP layer before they are compressed segmented and transmitted to the LLC layer. "
  但这时用户离开了当前的RA，因此，这个N-PDU仍停留在SNDCP层的缓存中，没有来得及发给用户，用户就到了新的RA。因为Old SGSN需要给New SGSN发送这个N-PDU，这个N-PDU是要交给New SGSN的SNDCP层处理的。即使是通过GTP-U的隧道传递，但仍应该使用N-PDU合适。否则在阅读规范的时候容易让人产生误解。感觉好像是下行数据GGSN发给SGSN似的。用N-PDU就代表的是用户原始的已经到达SGSN暂未发给用户的停留在缓存中的数据，和GGSN发给SGSN的用户数据T-PDU以示区别。
  个人感觉是这样。