无线网络-LTE (08) 通信过程之 Detach procedure HSS-initiated
operator-determined purposes to request the removal of a subscriber's MM and EPS bearer at the MME and
also at the SGSN if both an MME and an SGSN are registered in the HSS.
For subscription change, e.g. RAT restrictions to disallow one of the RATs, the Insert Subscription Data procedure
shall be used towards the MME, and also towards the SGSN if both an MME and an SGSN are registered in the HSS.
This procedure is not applied if a Cancel Location is sent to the MME or the SGSN with a cause other than Subscription Withdrawn.
HSS-Initiated去附着过程是由HSS发起的。通过这个过程的主要目的是可以由运营者决定是否删除MME上的MM的订阅和EPS承载。
当然如果SGSN和MME同时注册在HSS中时，他们的相关内容都会被删除。
Step 1
If the HSS wants to request the immediate deletion of a subscriber's MM contexts and EPS Bearers,
the HSS shall send a Cancel Location (IMSI, Cancellation Type) message with Cancellation Type set to
Subscription Withdrawn to the registered MME and also to the SGSN if an SGSN is also registered.
如果HSS希望立即删除订阅的 MM上下文和EPS承载，HSS 可以通过发送Cancel Location (IMSI, Cancellation Type)
到已注册的MME或SGSN来实现，需要把Cancellation Type设置为Subscription Withdrawn。
Step 2
If Cancellation Type is Subscription Withdrawn, the MME/SGSN which has an active UE context informs the
UE which is in ECM-CONNECTED state, that it has been detached, by sending Detach Request message to the UE.
If the UE is in ECM-IDLE state the MME pages the UE.
NOTE 4: The UE will receive only one Detach Request message in the RAT where it currently camps on.
如果Cancellation Type是Subscription Withdrawn， 如果MME/SGSN和手机间有个激活的UE 上下文，
当手机处于ECM-CONNECTED时，MME/SGSN 会发送Detach Request通知手机这个UE 上下文已经被去激活了。
如果手机处于ECM-IDLE 状态，MME会对手机发起寻呼。
Step 3
a.If the MME has an active UE context, the MME sends a Delete Session Request (TEID) message per PDN
connection to the Serving GW to deactivate the EPS Bearer Context information in the Serving GW.
如果MME有一个激活的手机上下文，MME会发送Delete Session Request (TEID)到S GW来去激活S GW上的EPS 承载上下文。
b.If the SGSN has an active UE context, the SGSN sends a Delete Session request (TEID) per PDN connection
to the Serving GW to deactivate the EPS Bearer Context information in the Serving GW.
如果SGSN有一个激活的手机上下文，SGSN会发送Delete Session Request (TEID)到S GW来去激活S GW上的EPS 承载上下文。
Step 4
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 in step 7.
When the S GW receives one or several Delete Session Request message(s) from the MME or SGSN in
ISR deactivated state, the Serving GW releases the related EPS Bearer context information and 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.
当S GW在ISR激活状态下收到第一个Delete Session Request 由MME或SGSN发来的消息时，Serving GW去激活 ISR
释放相关的EPS承载的上下文信息，并且在step 7 返回Delete Session Response来进行响应。
当S GW在ISR去激活状态下，收到从MME或SGSN发来的一条或多条Delete Session Request消息时，Serving GW
释放EPS承载上下文的信息并且发送Delete Session Request (TEID)到PDN GW.消息中包含了一个标识，
所有属于这个PDN连接的承载都会被释放掉。
Step 5
The PDN GW acknowledges with Delete Session Response (TEID) message.
PDN GW通过Delete Session Response (TEID)来进行响应。
Step 6
The PDN GW employs a PCEF initiated IP CAN Session Termination procedure as defined in TS 23.203 [6]
with the PCRF to indicate to the PCRF that the EPS bearer is released if a PCRF is configured.
如果配置了PCRF，PDN GW会启动一个PCEF initiated IP CAN Session Termination过程(TS 23.203 [6]中定义)
来通知PCRF EPS承载已经被释放了。
Step 7
The Serving GW acknowledges with Delete Session Response (TEID) message.
Serving GW通过发送Delete Session Response (TEID) 来响应Delete Session Request。
Step 8
If the UE receives the Detach Request message from the MME/SGSN, the UE sends a Detach Accept message
to the MME/SGSN any time after step 2. The message is sent either in E-UTRAN or GERAN/UTRAN access depending
on which access the UE received the Detach Request. For the Detach Accept message from UE to MME the eNodeB
forwards this NAS message to the MME along with the TAI+ECGI of the cell which the UE is using.
如果手机收到了从MME/SGSN发来的Detach Request消息时，手机会发送Detach Accept来进行响应。
消息可能通过E-UTRAN 或 GERAN/UTRAN进行发送，这取决于手机是通过哪个网络接收的 Detach Request 消息。
关于手机发送到MME的Detach Accept 消息，eNodeB会根据手机使用的TAI+ECGI 向 MME 进行转发。
Step 9
The MME/SGSN confirms the deletion of the MM contexts and the EPS Bearer(s) with a Cancel Location Ack (IMSI)
message to the HSS.
MME/SGSN会通过向HSS发送Cancel Location Ack (IMSI)来确认MM上下文和EPS承载已经被删除了。
Step 10
a. After receiving the Detach Accept message, the MME releases the S1-MME signalling connection for the UE
by sending S1 Release Command (Cause) message to the eNodeB with Cause set to Detach. The details of this step are
covered in the "S1 Release Procedure", as described in clause 5.3.5.
在收到了Detach Accept 消息后，MME会通过发送S1 Release Command (Cause=Detach) 来释放手机和eNodeB间的S1-MME信令连接。
b. After receiving the Detach Accept message, if Detach Type did not request the UE to make a new attach,
then the 3G SGSN releases the PS signalling connection
在收到了Detach Accept 消息后，如果Detach Type并没有要求手机建立一个新的附着，3G SGSN 会释放PS的信令连接。