Section: 5.3.8.4 HSS-initiated Detach procedure
Content: The HSS-Initiated Detach procedure is initiated by the HSS. The HSS uses this procedure for 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 UEs with emergency EPS bearers, the MME/SGSN shall not initiate detach procedure. Instead the MME/SGSN shall deactivate all the non-emergency PDN connection. If the HSS-Initiated Detach procedure is initiated, and UE is RLOS attached, the MME shall not initiate detach procedure. NOTE 1: HSS-initiated Detach can happen for a UE that camps on a cell in limited state due to UE moving to a forbidden area performs RLOS attach and the MME does not perform Purge procedure for the UE towards the HSS (as specified in clause 5.3.9.3). 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This procedure is not applied if a Cancel Location is sent to the MME or the SGSN with a cause other than Subscription Withdrawn. The HSS-Initiated Detach Procedure is illustrated in Figure 5.3.8.4-1. Figure 5.3.8.4-1: HSS-Initiated Detach Procedure NOTE 2: For a PMIP-based S5/S8, procedure steps (A) are defined in TS 23.402[ Architecture enhancements for non-3GPP accesses ]  [2]. Steps 4, 5 and 6 concern GTP based S5/S8. NOTE 3: Procedure steps (B) are used by the procedure steps (F) in clause 5.3.2.1. NOTE 4: The steps below apply for an S4-SGSN. For Gn/Gp SGSN, the procedure specified in clause 6.6.2.2. of TS 23.060[ General Packet Radio Service (GPRS); Service description; Stage 2 ]  [7] applies for the SGSN. 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the HSS shall send a Cancel Location (IMSI, Cancellation Type) message with Cancellation Type set to Subscription Withdrawn to the registered MME and also to the SGSN if an SGSN is also registered. When receiving the Cancel Location Message the MME/SGSN acknowledges with a Cancel Location ACK (IMSI) message to the HSS. 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 If Cancellation Type is Subscription Withdrawn, the MME/SGSN which has an active UE context informs the UE which is in ECM-CONNECTED state, that it has been detached, by sending Detach Request (Detach Type) message to the UE. If the Cancel Location message includes a flag to indicate re-attach is required, the MME/SGSN shall set the Detach Type to indicate that re-attach is required. If the UE is in ECM-IDLE state the MME pages the UE. NOTE 5: The UE will receive only one Detach Request message in the RAT where it currently camps on. 3a. If the UE has no activated PDN connection, then steps 3 to 7 are not executed. If the PLMN has configured secondary RAT usage data reporting, the MME shall wait for Step 8a, if applicable, and perform step 10a before step 3a. If the MME has an active UE context, for any PDN connection to the SCEF, the MME indicates to the SCEF that the PDN connection for the UE is no longer available according to TS 23.682[ Architecture enhancements to facilitate communications with packet data networks and applications ]  [74] and steps 3 to 7 are not executed. For PDN connections to the P-GW, the MME sends a Delete Session Request (LBI, User Location Information (ECGI), NAS Release Cause if available, Secondary RAT usage data if available, PSCell ID if available) message per PDN connection to the Serving GW to deactivate the EPS Bearer Context information in the Serving GW. NAS Release Cause is only sent by the MME to the PDN GW if this is permitted according to MME operator's policy. If MME has received PSCell ID from eNodeB, the MME includes it in Delete Session Request. 3b. If the SGSN has an active UE context, the SGSN sends a Delete Session Request (LBI, User Location Information (CGI/SAI)) per PDN connection to the Serving GW to deactivate the EPS Bearer Context information in the Serving GW. 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 (LBI, User Location Information (ECGI or CGI/SAI), NAS Release Cause if available, Secondary RAT usage data if PGW secondary RAT usage data reporting is active) message for each associated PDN connection to the PDN GW. NAS Release Cause is the one received in the Delete Session Request from the MME or SGSN. This message indicates that all bearers belonging to that PDN connection shall be released. If the UE Time Zone has changed, the MME includes the UE Time Zone IE in this message. If the MME and/or SGSN sends UE's Location Information and/or UE Time Zone Information in step 3a and/or step 3b, the S-GW includes the User Location Information and/or UE Time Zone with the least age in this message. 5. The PDN GW acknowledges with Delete Session Response (Cause and, optionally, APN Rate Control Status according to clause 4.7.7.3) message. 6. The PDN GW employs a PCEF initiated IP-CAN Session Termination procedure as defined in TS 23.203[ Policy and charging control architecture ]  [6] with the PCRF to indicate to the PCRF that the EPS bearer is released if a PCRF is configured. If requested by the PCRF the PDN GW indicates User Location Information and/or UE Time Zone Information and NAS Release Cause (if available) to the PCRF as defined in TS 23.203[ Policy and charging control architecture ]  [6]. 7. The Serving GW acknowledges with Delete Session Response (TEID and, optionally, APN Rate Control Status) message. If received, the MME stores the APN Rate Control Status in the MM context. 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. If Dual Connectivity is active for the UE, the PSCell ID shall be included in the Uplink NAS Transport that carries the Detach Accept message. 9. Void. 10a. 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. NOTE 6: In the "S1 Release Procedure", if Dual Connectivity was active at the time of the release, the eNodeB includes the PSCell ID. 10b. 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.