无线网络-LTE (07) 通信过程之 Detach procedure MME-initiated
Step 1
The MME initiated detach procedure is either explicit (e.g. by O&M intervention) or implicit. The MME may implicitly detach a UE, if it has not had communication with UE for a long period of time. The MME does not send the Detach Request (Detach Type) message to the UE for implicit detach. The implicit detach is local to the MME, i.e. an SGSN registration will not be detached. If the UE is in ECM-CONNNECTED state the MME may explicitly detach the UE by sending a Detach Request message to the UE. The Detach Type may be set to re-attach in which case the UE should re-attach at the end of the detach process. If the UE is in ECM-IDLE state the MME pages the UE.
MME可以显式或隐式的执行detach 的过程。如果UE长时间和网络间没有通信，MME会执行隐式的detach过程。在执行隐式的detach过程时，MME不向手机端发送Detach Request(Detach Type) 消息。隐式的detach过程是在MME本地执行的，它不会影响其他网元，例如：SGSN的注册是不会被去附着的。如果手机是在ECM-CONNNECTED状态，MME可能会执行显式的Detach 过程，向手机发送Detach Request消息。如果希望手机在detach后可以重新attach到网络中，可以把Detach Type 设置为re-attach。
如果手机是在ECM-IDLE 状态， MME则会向手机发起寻呼 (Paging)。
Step 2
Any EPS Bearer Context information in the Serving GW regarding this particular UE and related to the MME are deactivated by the MME sending Delete Session Request (TEID) message per PDN connection to the Serving GW. If the PDN GW requested UE's location info, the MME also includes the User Location Information IE in this message.
MME会向Serving GW发送Delete Session Request (TEID)消息，此时在Serving GW和该手机和MME相关的 EPS Bearer Context 则会被去激活。如果PDN GW需要该手机的位置信息，MME会在消息中包含User Location Information。
Step 3
When the S-GW receives the first Delete Session Request message from the MME or SGSN in ISR activated state, the Serving GW deactivates ISR, releases the related EPS Bearer context information and responds with Delete Session Response (TEID). When the S GW receives the Delete Session Request message from the MME or SGSN in ISR deactivated state, the Serving GW releases the related EPS Bearer context information and jumps to step 6 by sending a Delete Session Request (TEID) message to the PDN GW. After step 7 the Serving GW responds back to the MME/SGSN with the Delete Session Response (TEID) message.当S-GW从MME收到了第一条Delete Session Request消息，或者SGSN处于ISR 激活状态，Serving GW会去激活ISR，并且释放相关的EPS Bearer上下文的信息，返回Delete Session Response (TEID) 消息。
当S-GW从MME收到了Delete Session Request消息，或者SGSN处于ISR 去激活状态，Serving GW会释放相关的EPS Bearer上下文的信息并且执行Step 6，发送Delete Session Request (TEID) 消息到PDN GW。并且在Step 7 后，Serving GW 向MME/SGSN返回Delete Session Response (TEID)消息。
Step 4
If ISR is activated, MME sends Detach Notification (Cause) message to the associated SGSN. The cause indicates whether it is a local or complete detach.
如果 ISR是被激活的，MME会发送Detach Notification (Cause)消息到关联的 SGSN。消息中 "cause" 会说明它是一个本地的或完全的detach过程。
Step 5
If cause indicates complete detach then the SGSN sends a Delete Session Request (TEID) message per PDN connection to the Serving GW. If Cause indicates local detach then SGSN deactivates ISR and steps 5 to 9 shall be skipped. If the PDN GW requested UE's location info, the SGSN also includes the User Location Information IE in this message.
如果"Cause"标识出是一个完全的 detach过程，SGSN会向Serving GW发送Delete Session Request (TEID)消息。如果是本地detach过程，SGSN 会去激活ISR，并且 Step 5 到 Step 9会被省略。如果PDN GW请求UE的位置信息，SGSN在发送的消息中会包括User Location Information的数据。
Step 6
If ISR is activated, Serving GW deactivates ISR.If ISR is not activated and the Serving GW received one or several Delete Session Request message(s) from SGSN in step 2, the Serving GW sends a Delete Session Request (TEID) message for each associated PDN connection to the PDN GW. This message includes an indication that all bearers belonging to that PDN connection shall be released.If the MME and/or SGSN send(s) UE's Location Information in step 2 and/or Step 5, the S GW includes the User Location Information with the least age in this message.
如果ISR是处于激活状态的，Serving GW会去激活ISR。如果ISR是未被激活的，并且Serving GW从SGSN收到了一个或多个Delete Session Request (TEID)消息。Serving GW 会发送Delete Session Request (TEID)到PDN GW。消息会包含标识去释放所有相关的PDN 连接。如果MME 和/或 SGSN 在Step2 和/或 Step5 发送了手机的位置信息，那么S GW的消息中就需要发送最新的手机位置信息。
Step 7
The PDN GW acknowledges with Delete Bearer Response (TEID) message.
PDN GW 通过Delete Bearer Response (TEID)来进行响应。
Step 8
The PDN GW employs an IP CAN Session Termination procedure as defined in TS 23.203 [6] with the PCRF to indicate to the PCRF that the EPS Bearer(s) are released if a PCRF is configured.
如果网络中配置了 PCRF，PDN GW会通过一个IP CAN Session Termination(TS 23.203 [6]定义)过程
来通知PCRF释放EPS的承载。
Step 9
The Serving GW acknowledges with Delete Session Response (TEID) message.
Serving GW通过Delete Session Response (TEID)消息来响应请求。
Step 11
The SGSN sends Detach Acknowledge message to the MME.
SGSN 发送Detach Acknowledge消息到MME。
Step 12
If the UE receives the Detach Request message from the MME in the step 1, the UE sends a Detach Accept message to the MME any time after step 1. The eNodeB forwards this NAS message to the MME along with the TAI+ECGI of the cell which the UE is using.
如果手机接收到了从MME发来的Detach Request消息 (Step 1)，在Step 1 以后的任何时间点，手机会发送Detach Accept给 MME，eNodeB 根据TAI+ECGI 会向 MME转发这个来自手机的消息。
Step 13
After receiving the Detach Accept message, Delete Session Response and, if appropriate, Detach Acknowledge message, the MME releases the S1-MME signalling connection for the UE by sending an S1 Release Command (Cause) message to the eNodeB. The details of this step are covered in the "S1 Release Procedure", as described in clause 5.3.5 by step 4 to step 6. If the Detach Type requests the UE to make a new attach, the UE reattaches after the RRC Connection Release is completed.
当MME收到了 Detach Accept, Delete Session Response 和对应的Detach Acknowledge消息后，MME会通过发送S1 Release Command (Cause) 到eNodeB 来释放该手机的 S1-MME信令连接。在"S1 Release Procedure"5.3.5章节中我们可以找到详细的信令流程。如果 Detach Type 要求手机重新建立一个新的附着，手机会在RRC Connection Release完成后重新进行附着。
Step 14
After the MME receives the Delete Session Response from Serving GW, if the subscription data indicates that the user is allowed to perform handover to non-3GPP access and the MME is configured to notify the HSS at detach, the MME shall send a Notify Request to indicate that the HSS shall remove the APN and PDN GW identity pairs for this UE.
Step 15
The HSS removes all APN and PDN GW identity pairs that were dynamically stored and sends a Notify Response to the MME
HSS删除了所有该手机的APN 和 PDN GW标识后发送Notify Response到MME。