5.3.8 Detach procedure

23.4013GPPGeneral Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access Network (E-UTRAN) accessRelease 18TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

5.3.8.1 General

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 two 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.

5.3.8.2 UE-initiated Detach procedure

The Detach procedure when initiated by the UE is described in clauses 5.3.8.2.1 and 5.3.8.2.2.

5.3.8.2.1 UE-initiated Detach procedure for E-UTRAN

Figure 5.3.8.2-1 shows the case when UE camps on E-UTRAN and Detach Request is sent to MME.

Figure 5.3.8.2-1: UE-Initiated Detach Procedure – UE camping on E-UTRAN

NOTE 1: For a PMIP-based S5/S8, procedure steps (A) are defined in TS 23.402 [2]. Steps 6, 7 and 8 concern GTP based S5/S8

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.

If the MME receives a Detach Request via a CSG cell with Switch Off parameter indicating that detach is not due to a switch off situation, and the CSG subscription for this CSG ID and associated PLMN is absent or expired, the MME shall trigger a MME-initiated Detach procedure as specified in clause 5.3.8.3.

If Dual Connectivity is active for the UE, the PSCell ID shall be included in the Uplink NAS Transport that carries the Detach Request message.

NOTE 2: Security procedures may be invoked if the NAS message is used to establish the S1 connection.

NOTE 3: For emergency attached or RLOS attached UEs that were not successfully authenticated, security procedures are not performed.

2. If the UE has no activated PDN connection, then steps 2 to 10 are not executed. If the PLMN has configured secondary RAT usage data reporting, the MME shall wait for step 11, if applicable, and shall perform step 12 before step 2 onwards. 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 [74] and steps 2 to 10 are not executed. For PDN connections to the P-GW, the active EPS Bearers in the Serving GW regarding this particular UE are deactivated by the MME sending Delete Session Request (LBI, User Location Information (ECGI), Secondary RAT usage data, PSCell ID) 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 UE Time Zone has changed, the MME includes the UE Time Zone IE in this message. If Secondary RAT usage data report was received from RAN, the MME includes this in the Delete Session Request message. If MME has received PSCell ID from eNodeB, the MME includes it in Delete Session Request.

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 (Cause).

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 (LBI) 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 (Cause and, optionally, APN Rate Control Status according to clause 4.7.7.3) message.

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

5. The active PDP contexts in the Serving GW regarding this particular UE are deactivated by the SGSN sending Delete Session Request (LBI, CGI/SAI) per PDN connection to the Serving GW. If the UE Time Zone has changed, the SGSN includes the UE Time Zone IE in this message.

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 (LBI, User Location Information (ECGI or CGI/SAI), Secondary RAT usage data) per PDN connection to the PDN GW. If ISR is not activated, this step shall be triggered by step 2. This message indicates that all bearers belonging to that PDN connection shall be released. If the MME and/or SGSN sends UE’s Location Information, and/or UE Time Zone Information, and/or Secondary RAT usage data in step 2 and/or step 5, the S‑GW includes the User Location Information, and/or UE Time Zone, and/or User CSG Information with the least age in this message and/or Secondary RAT usage data information.

7. The PDN GW acknowledges with Delete Session Response (Cause and, optionally, APN Rate Control Status according to clause 4.7.7.3).

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. If requested by the PCRF the PDN GW indicates User Location Information and/or UE Time Zone Information to the PCRF as defined in TS 23.203 [6].

9. The Serving GW acknowledges with Delete Session Response (Cause and, optionally, APN Rate Control Status).

10. The SGSN sends Detach Acknowledge message to the MME (optionally APN Rate Control Status). If received, the MME stores the APN Rate Control Status in the MM context.

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

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.

NOTE 4: In the "S1 Release Procedure", if Dual Connectivity was active at the time of the release, the eNodeB includes the PSCell ID.

5.3.8.2.2 UE-initiated Detach procedure for GERAN/UTRAN with ISR activated

Figure 5.3.8.2-2 shows the case when UE with ISR Activated camps on GERAN/UTRAN and Detach Request is sent to SGSN. Refer to clause 6.6.1 of TS 23.060 [7] for the UE-initiated Detach procedure when ISR is not activated.

Figure 5.3.8.2-2: UE-Initiated Detach Procedure – UE camping on GERAN/UTRAN, ISR activated

1. The UE sends NAS message Detach Request (Detach Type, P‑TMSI, P‑TMSI‑Signature, Switch Off) to the SGSN. Detach Type indicates which type of detach is to be performed, i.e. GPRS Detach only, IMSI Detach only or combined GPRS and IMSI Detach. Switch Off indicates whether detach is due to a switch off situation or not. The Detach Request message includes P‑TMSI and P‑TMSI Signature. P‑TMSI Signature is used to check the validity of the Detach Request message. If P‑TMSI Signature is not valid or is not included, the authentication procedure should be performed.

If the SGSN receives a Detach Request via a CSG cell with Switch Off parameter indicating that detach is not due to a switch off situation, and the CSG subscription for this CSG ID and associated PLMN is absent or expired, the SGSN shall trigger a SGSN-initiated Detach procedure as specified in clause 5.3.8.3A.

2. The active EPS Bearers in the Serving GW regarding this particular UE are deactivated by the SGSN sending Delete Session Request (LBI, User Location Information (CGI/SAI)) per PDN connection to the Serving GW. Because ISR is activated, then the Serving GW shall not release the Control Plan TEID allocated for MME/SGSN until it receives the Delete Session Request message in step 5. If the UE Time Zone has changed, the SGSN includes the UE Time Zone IE in this message.

3. Because the Serving GW receives this message in ISR activated state, the Serving GW deactivates ISR and acknowledges with Delete Session Response (Cause).

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

5. The active PDP contexts in the Serving GW regarding this particular UE are deactivated by the MME sending Delete Session Request (LBI, ECGI) per PDN connection to the Serving GW. If the UE Time Zone has changed, the MME includes the UE Time Zone IE in this message.

6. Serving GW deactivates ISR and sends Delete Session Request (LBI, User Location Information (ECGI or CGI/SAI)) per PDN connection to the PDN GW. If ISR is not activated, this step shall be triggered by step 2. This message indicates that all bearers belonging to that PDN connection shall be released. If the MME and/or SGSN sends UE’s Location Information and/or UE Time Zone Information in step 2 and/or step 5, the S‑GW includes the User Location Information and/or UE Time Zone with the least age in this message.

7. The PDN GW acknowledges with Delete Session Response (Cause).

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. If requested by the PCRF the PDN GW indicates User Location Information and/or UE Time Zone Information to the PCRF as defined in TS 23.203 [6].

9. The Serving GW acknowledges with Delete Session Response (Cause).

10. The MME sends Detach Acknowledge message to the SGSN.

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

12. If the MS was GPRS detached, then the 3G SGSN releases the PS signalling connection.

5.3.8.3 MME-initiated Detach procedure

The MME-Initiated Detach procedure when initiated by the MME is illustrated in Figure 5.3.8.3-1.

This procedure may be also used as part of the SIPTO function when the MME determines that GW relocation is desirable for all PDN connection(s) serving SIPTO-allowed APNs. The MME initiates the "explicit detach with reattach required" procedure and the UE should then re-establish those PDN connections for the same APN(s).

Figure 5.3.8.3-1: MME-Initiated Detach Procedure

NOTE 1: For a PMIP-based S5/S8, procedure steps (A) are defined in TS 23.402 [2]. Steps 3, 4 and 5 concern GTP based S5/S8.

NOTE 2: Procedure steps (B) are used by the procedure steps (E) in clause 5.3.2.1.

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.

For emergency attached UEs, MME initiated implicit detach procedures are based on an inactivity timeout specific to emergency.

If this Detach procedure is due to the UE’s Detach Request via a CSG cell which the UE is not allowed to access, i.e. the CSG subscription for this CSG ID and associated PLMN is absent or expired, the MME shall send a Detach Request to UE with an appropriate cause indicating the UE is not allowed to access this CSG.

In the case of satellite access for Cellular IoT, the MME initiates detach procedure if it detects that the UE’s registered PLMN is not allowed to operate in the present UE location (see clause 4.13.4). In this case, the MME shall include in the Detach Request message a suitable cause value.

2. If the UE has no activated PDN connection, then steps 2 to 10 are not executed. If the PLMN has configured secondary RAT usage reporting, the MME shall wait for step 11, if applicable, and perform step 12 before step 2 onwards. For any PDN connections 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 [74] and steps 2 to 10 are not executed. For PDN connections to the P-GW, 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 (LBI, User Location Information (ECGI), NAS Release Cause if available, Secondary RAT usage data, PSCell ID) message per PDN connection to the Serving GW. If the UE Time Zone has changed, the MME includes the UE Time Zone IE in this message. NAS Release Cause is only sent by the MME to the PDN GW if this is permitted according to MME operator’s policy. If Secondary RAT usage data report was received from the RAN, the MME includes this in the Delete Session Request message. If MME has received PSCell ID from eNodeB, the MME includes it in Delete Session Request.

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 (LBI) message to the PDN GW. After step 7 the Serving GW responds back to the MME/SGSN with the Delete Session Response (Cause and, optionally, APN Rate Control Status according to clause 4.7.7.3) message.

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.

5. If cause indicates complete detach then the SGSN sends a Delete Session Request (LBI, CGI/SAI) 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 UE Time Zone has changed, the SGSN includes the UE Time Zone IE in this message.

6. If ISR is activated, Serving GW deactivates ISR.

If ISR is not activated and the Serving GW received one or several Delete Bearer Request message(s) from SGSN in step 2, the Serving GW sends a Delete Session Request (LBI, User Location Information (ECGI or CGI/SAI), NAS Release Cause if available, Secondary RAT usage data) 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. This message indicates that all bearers belonging to that PDN connection shall be released.

If the MME and/or SGSN send(s) UE’s Location Information, and/or UE Time Zone and/or Secondary RAT usage data in step 2 and/or step 5, the S‑GW includes the User Location Information, and/or UE Time Zone Information with the least age in this message and/or Secondary RAT usage data.

7. The PDN GW acknowledges with Delete Session Response (Cause and, optionally, APN Rate Control Status according to clause 4.7.7.3) message.

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. 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 [6].

9. The Serving GW acknowledges with Delete Session Response (Cause, APN Rate Control Status) message.

10. The SGSN sends Detach Acknowledge message to the MME (APN Rate Control Status). The MME stores the APN Rate Control Status in the MM context.

11. 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.

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.

If the UE receives Detach Request from the MME via a CSG cell with the cause indicating the UE is not allowed to access this CSG, the UE shall remove this CSG ID and associated PLMN from its Allowed CSG list, if present.

12. 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.

NOTE 3: In the "S1 Release Procedure", if Dual Connectivity was active at the time of the release, the eNodeB includes the PSCell ID.

5.3.8.3A SGSN-initiated Detach procedure with ISR activated

The SGSN-Initiated Detach procedure with ISR activated is illustrated in Figure 5.3.8.3A-1. Refer to clause 6.6.2.1 of TS 23.060 [7] for the SGSN-initiated Detach procedure when ISR is not activated.

Figure 5.3.8.3A-1: SGSN-Initiated Detach Procedure with ISR activated

NOTE 1: For a PMIP-based S5/S8, procedure steps (A) are defined in TS 23.402 [2]. Steps 3, 4 and 5 concern GTP based S5/S8.

1. The SGSN initiated detach procedure is either explicit (e.g. by O&M intervention) or implicit. The SGSN may implicitly detach a UE, if it has not had communication with UE for a long period of time. The SGSN does not send the Detach Request (Detach Type) message to the UE for implicit detach. The implicit detach is local to the SGSN, i.e. an MME registration will not be detached. If the UE is in PMM-CONNNECTED state the SGSN 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 PMM-IDLE state the SGSN pages the UE.

If this Detach procedure is due to the UE’s Detach Request via a CSG cell which the UE is not allowed to access, i.e. the CSG subscription for this CSG ID and associated PLMN is absent or expired, the SGSN shall send a Detach Request to UE with an appropriate cause indicating the UE is not allowed to access this CSG.

2. Any EPS Bearer Context information in the Serving GW regarding this particular UE and related to the SGSN is deactivated by the SGSN sending Delete Session Request (LBI, User Location Information (ECGI)) message per PDN connection to the Serving GW. If the UE Time Zone has changed, the SGSN includes the UE Time Zone IE in this message.

3. Because the Serving GW receives this message in ISR activated state, the Serving GW deactivates ISR, releases the SGSN related EPS Bearer context information and acknowledges with Delete Session Response (Cause).

4. Because ISR is activated, the SGSN sends Detach Notification (Cause) message to the associated MME. The cause indicates whether it is a local or complete detach.

5. If cause indicates complete detach then the MME sends a Delete Session Request (LBI, User Location Information (ECGI)) message per PDN connection to the Serving GW. If Cause indicates local detach then MME deactivates ISR and steps 5 to 9 shall be skipped. If the UE Time Zone has changed, the MME includes the UE Time Zone IE in this message.

6. The Serving GW sends a Delete Session Request (LBI, User Location Information (ECGI or CGI/SAI)) message per PDN connection to the PDN GW. This message indicates that all bearers belonging to that PDN connection shall be released. If the MME and/or SGSN sends UE’s Location Information and/or UE Time Zone in step 2 and/or step 5, the S‑GW includes the User Location Information and/or UE Time Zone Information with the least age in this message.

7. The PDN GW acknowledges with Delete Session Response (Cause) message.

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. If requested by the PCRF the PDN GW indicates User Location Information and/or UE Time Zone Information to the PCRF as defined in TS 23.203 [6].

9. The Serving GW acknowledges with Delete Session Response (Cause) message.

10. The MME sends Detach Acknowledge message to the SGSN.

11. If the UE receives the Detach Request message from the SGSN in the step 1, the UE sends a Detach Accept message to the SGSN any time after step 1.

If the UE receives Detach Request from the SGSN via a CSG cell with the cause indicating the UE is not allowed to access this CSG, the UE shall remove this CSG ID and associated PLMN from its Allowed CSG list, if present.

12. 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.

5.3.8.4 HSS-initiated Detach procedure

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 [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 [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 [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 [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 [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.