无线网络-LTE (06) 通信过程之 Detach procedure UE-initiated

The Detach procedure allows:

- the UE to inform the network that it does not want to access the EPS any longer, and

- the network to inform the UE that it does not have access to the EPS any longer.

The UE is detached either explicitly or implicitly:

- Explicit detach: The network or the UE explicitly requests detach and signal with each other.

- Implicit detach: The network detaches the UE, without notifying the UE. This is typically the case when the network presumes that it is not able to communicate with the UE, e.g. due to radio conditions.

Four detach procedures are provided when the UE accesses the EPS through E-UTRAN. The first detach procedure is UE-initiated

detach procedure and other detach procedures are network-initiated detach procedure:

- UE-Initiated Detach Procedure. In the ISR activated case the UE initiated detach is split into to sub procedures, one for UE camping on E-UTRAN and one for UE camping on GERAN/UTRAN;

- MME-Initiated Detach Procedure;

- SGSN-Initiated Detach procedure with ISR activated;

- HSS-Initiated Detach Procedure.

NOTE 1: The MME and the UE may enter EMM-DEREGISTERED state without the above procedures.

Detach 过程发生情况：

- 手机通知网络它不再需要接入EPS

- 网络通知手机它不再接入EPS

手机可以明确的进行Detach 或 暗示的Detach

- 明确 detach: 网络或手机明确的要求detach和信令

- 暗示 detach: 网络detach手机，但不通知手机。通常发生在网络假设它无法和手机通信，例如无线信号问题。

Detach 过程有4种 第一种是手机发起的，其他是由网络发起的

- UE-Initiated Detach Procedure

- MME-Initiated Detach Procedure;

- SGSN-Initiated Detach procedure with ISR activated;

- HSS-Initiated Detach Procedure.

UE-initiated Detach procedure for E-UTRAN



Step 1

The UE sends NAS message Detach Request (GUTI, Switch Off) to the MME. This NAS message is used to trigger the establishment of the S1 connection if the UE was in ECM-IDLE mode. Switch Off indicates whether detach is due to a switch off situation or not. The
eNodeB forwards this NAS message to the MME along with the TAI+ECGI of the cell which the UE is using. NOTE 2: Security procedures may be invoked if the NAS message is used to establish the S1 connection.

手机发送NAS:Detach Request到MME。如果手机是ECM-IDLE 模式，此消息用来触发S1连接建立。Switch Off 标识出detach是否是由于switch off状态引起的。eNodeB转发这个NAS消息到MME，并且附上手机使用的TAI+ECGI。

Step 2

The active EPS Bearers in the Serving GW regarding this particular UE are deactivated by the MME sending Delete Session Request (TEID) per PDN connection to the Serving GW. If ISR is activated, then the Serving GW shall not release the Control Plane TEID allocated
for MME/SGSN until it receives the Delete Session Request message in step 5. If the PDN GW requested UE's location info, the MME also includes the User Location Information IE in this message.

MME通过每个PDN的连接会发送Delete Session Request (TEID)到Serving GW, 使在Serving GW上激活的EPS承载认为这部手机处于去激活状态。

如果ISR被激活，Serving GW不应该释放为MME/SGSN分配的Control Plane TEID直到收到Delete Session Request。

如果PDN GW请求手机的位置信息，MME在消息中应该也包含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 per PDN connection 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收到第一个从MME 或 SGSN发出的Delete Session Request(ISR为激活状态)时，Serving GW去激活ISR，释放相关的EPS承载上下文信息并且

发送Delete Session Response作为响应。当S GW从MME或SGSN收到Delete Session Request并且ISR为去激活状态时，Serving GW释放

相关EPS承载的上下文信息，并且通过PDN 连接发送Delete Session Request到PDN GW。

Step 4

If ISR is activated, MME sends Detach Notification (Cause) message to the associated SGSN. The Cause indicates complete detach.

Step 5

The active PDP contexts in the Serving GW regarding this particular UE are deactivated by the SGSN sending Delete Session Request (TEID) per PDN connection to the Serving GW. If the PDN GW requested UE's location info, the SGSN also includes the User Location
Information IE in this message.

Serving GW会收到SGSN发送的Delete Session Request (TEID)，使激活的PDP上下文认为该手机为去激活状态。

Step 6

If ISR is activated, Serving GW deactivates ISR. If ISR is not activated in the Serving GW, the Serving GW sends Delete Session Request (TEID) per PDN connection to the PDN GW. If ISR is not activated, this step shall be triggered by step 2. This message includes
an indication that all bearers belonging to that PDN connection shall be released. If the MME and/or SGSN sends 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被激活了，Serving GW 则去激活ISR。如果SIR在Serving GW没有被激活，Serving GW 会通过PDN连接发送Delete Session Request到PDN GW。

Step 7

The PDN GW acknowledges with Delete Bearer Response (TEID).

Step 8

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 EPS Bearer is released if PCRF is applied in the network.

Step 9

The Serving GW acknowledges with Delete Session Response (TEID).

Step 10

The SGSN sends Detach Acknowledge message to the MME.

Step 11

If Switch Off indicates that detach is not due to a switch off situation, the MME sends a Detach Accept to the UE.

Step 12

The MME releases the S1-MME signalling connection for the UE by sending S1 Release Command 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.

手机通过发送S1 Release Command原因: Detach，MME释放了S1-MME信令连接。

Step 13

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.

当MME收到从Serving GW 返回的Delete Session Response后，

Step 14

The HSS removes all APN and PDN GW identity pairs that were dynamically stored and sends a Notify Response to the MME.