Content for TS 29.118 Word version: 18.0.0

5.4 Explicit IMSI detach from EPS services p. 31

5.4.1 General description p. 31

This procedure is used by the MME to indicate to the VLR that the UE has been detached from EPS services and therefore the SGs association between the MME and the VLR has to be deactivated. This procedure only applies to UEs which are not in the SGs-NULL state at the MME. The procedures specified in this subclause apply to EPS detach indication initiated by the UE or by the network as specified in TS 24.301.

The procedure is also used by the MME to indicate to the VLR when a combined tracking area update procedure has been rejected by the MME, except when the MME performs the NAS level mobility management congestion control as specified in TS 24.301, or the MME receives the Detach Notification from the SGSN, as described in TS 29.274, when Idle mode Signalling Reduction is activated.

The procedure is also used by the MME to indicate to the VLR when a periodic tracking area update procedure has been rejected by the MME, except when the MME performs the NAS level mobility management congestion control as specified in TS 24.301, for a UE for which an SGs association exists.

The Explicit IMSI detach from EPS services procedure aborts any other ongoing procedure related to this UE on the SGs interface in the MME and in the VLR.

5.4.2 Procedures in the MME p. 31

5.4.2.1 Explicit EPS detach initiation p. 31

The MME shall send an SGsAP-EPS-DETACH-INDICATION message to a VLR if:

the MME receives a detach for EPS from the UE;
the MME performs network initiated EPS detach procedure;
the combined tracking area update procedure is rejected by the MME, except when the MME performs the NAS level mobility management congestion control as specified in TS 24.301;
the periodic tracking area update procedure is rejected by the MME, except when the MME performs the NAS level mobility management congestion control as specified in TS 24.301, for a UE for which an SGs association exists; or
the MME receives a Detach Notification from the SGSN with the Detach type indicating "PS Detach".

If the MME receives a Detach Request from a UE or Detach Notification from an SGSN and the state of the SGs association to a VLR for that UE is not SGs-NULL, the MME shall check the detach type indicated in the Detach Request message or the detach type indicated in the Detach Notification message. If the UE has indicated EPS detach the MME shall send an SGsAP-EPS-DETACH-INDICATION message to the VLR indicating "UE initiated IMSI detach from EPS services".

If the MME performs a network initiated detach procedure and the state of the SGs association to a VLR for that UE is not SGs-NULL, the MME shall send an SGsAP-EPS-DETACH-INDICATION message to the VLR indicating "Network initiated IMSI detach from EPS services".

If the combined or periodic tracking area update procedure is rejected at the MME, except when the MME performs the NAS level mobility management congestion control as specified in TS 24.301, for a UE with an SGs association state different from SGs-NULL, the MME shall send an SGsAP-EPS-DETACH-INDICATION to the VLR indicating "EPS services not allowed".

After sending of the SGsAP-EPS-DETACH-INDICATION message, the MME shall move the state of the SGs association to SGs-NULL. The MME shall start timer Ts8 upon transmission of the SGsAP-EPS-DETACH-INDICATION message and the MME shall stop and reset timer Ts6-1 if running.

5.4.2.2 Explicit EPS detach response p. 32

If the MME receives an SGsAP-EPS-DETACH-ACK message from the VLR, the MME shall stop timer Ts8. If a confirmation of the detach needs to be sent to the UE, the MME shall not wait for the reception of the SGsAP-EPS-DETACH-ACK message to send such confirmation.

5.4.2.3 Abnormal cases p. 32

If no SGsAP-EPS-DETACH-ACK message is received by the MME in response to a previous SGsAP-EPS-DETACH-INDICATION message before timer Ts8 expires, the MME shall repeat the SGsAP-EPS-DETACH-INDICATION message a maximum of Ns8 times.

5.4.3 Procedures in the VLR p. 32

When a VLR receives an SGsAP-EPS-DETACH-INDICATION message, the VLR shall send an SGsAP-EPS-DETACH-ACK message to the sending MME. The VLR shall check the MME name indicated in the SGsAP-EPS-DETACH-INDICATION message. If the received MME name is not changed comparing to the MME name stored in the VLR, the VLR shall move the state of the SGs association for the UE from any state to SGs-NULL and marks the SGs association as "detached for EPS services". Otherwise, the VLR shall not change the state of the SGs association.

If the VLR's implicit detach timer is not running then the VLR shall set and restart the implicit detach timer upon reception of an SGsAP-EPS-DETACH-INDICATION message. If the VLR's implicit detach timer is running (the state of the SGs association was already SGs-NULL) then the reception of an SGsAP-EPS-DETACH-INDICATION message shall not affect VLR's implicit detach timer.

5.5 Explicit IMSI detach from non-EPS services p. 32

5.5.1 General description p. 32

This procedure is used by the MME to indicate to the VLR that the UE has performed IMSI detach from non-EPS services and therefore the SGs association between the MME and the VLR has to be deactivated. This procedure applies only to UEs for which there is a SGs association at the MME. The procedures specified in this subclause apply only to IMSI detach request, combined IMSI and EPS detach requests from the UE or Detach Notification message from an SGSN.

The explicit IMSI detach from non-EPS services procedure aborts any other ongoing procedure related to this UE on the SGs interface in the MME and in the VLR.

In order to ensure that the VLR and the UE are synchronized as to which paging channel to use for any of the subsequent paging events, the MME shall attempt to inform the VLR about the detach event by using a retry scheme if the initial delivery of the SGsAP-IMSI-DETACH-INDICATION message fails.

5.5.2 Procedures in the MME p. 32

5.5.2.1 Explicit IMSI detach initiation p. 32

When an MME receives a Detach Request from a UE for which an SGs association exists, the MME shall check the detach type indicated. If the UE is indicating IMSI detach or combined EPS/IMSI detach, the MME shall send an SGsAP-IMSI-DETACH-INDICATION message to the VLR indicating "Explicit UE initiated IMSI detach from non-EPS services" or "Combined UE initiated IMSI detach from EPS and non-EPS services".

When an MME receives a Detach Notification message for a UE from an SGSN and an SGs association for the UE exists, the MME shall check the cause and detach type indicated. If the cause is indicating "IMSI Detach only", the MME shall send an SGsAP-IMSI-DETACH-INDICATION message to the VLR indicating "Explicit UE initiated IMSI detach from non-EPS services". If the cause is indicating "Complete Detach" and detach type is indicating "Combined PS/CS Detach" as specified in TS 29.274, the MME shall send an SGsAP-IMSI-DETACH-INDICATION message to the VLR indicating "Combined UE initiated IMSI detach from EPS and non-EPS services".

After the sending of the SGsAP-IMSI-DETACH-INDICATION message to the VLR, the MME shall move the state of the SGs association to SGs-NULL. The MME shall start timer Ts9 upon transmission of the SGsAP-IMSI-DETACH-INDICATION message and the MME shall stop and reset timer Ts6-1, if running.

5.5.2.2 Explicit IMSI detach response p. 33

If the MME receives an SGsAP-IMSI-DETACH-ACK message from the VLR, the MME shall stop timer Ts9. If the detach type received from the UE indicated IMSI only detach or combined EPS/IMSI detach not due to switch off, the MME shall wait for the reception of the SGsAP-IMSI-DETACH-ACK message before sending the confirmation of the detach to the UE.

5.5.2.3 Abnormal cases p. 33

The following abnormal cases can be identified:

no SGsAP-IMSI-DETACH-ACK received for a detach with switch off
If the MME sent an SGsAP-IMSI-DETACH-INDICATION message for a combined IMSI and EPS detach due to switch off and timer Ts9 expires, the MME shall repeat the SGsAP-IMSI-DETACH-INDICATION message a maximum of Ns9 times.
no SGsAP-IMSI-DETACH-ACK received for a detach with no switch off
If the MME sent an SGsAP-IMSI-DETACH-INDICATION message for an IMSI only detach or a combined IMSI and EPS detach not due to switch off and timer Ts9 expires, the MME shall repeat the SGsAP-IMSI-DETACH-INDICATION message a maximum of Ns9 times. If no SGsAP-IMSI-DETACH-ACK is received after that the MME shall send the confirmation of the detach to the UE.

5.5.3 Procedures in the VLR p. 33

When a VLR receives an SGsAP-IMSI-DETACH-INDICATION message, the VLR shall send an SGsAP-IMSI-DETACH-ACK message to the sending MME.

The VLR shall check the MME name indicated in the SGsAP-IMSI-DETACH-INDICATION message. If the received MME name is not changed comparing to the MME name stored in the VLR, the VLR shall move the state of the SGs association for the UE from any state to SGs-NULL. If the SGsAP-IMSI-DETACH-INDICATION message indicated "Explicit UE initiated IMSI detach from non-EPS services", the VLR marks the SGs association as "IMSI detached for non-EPS services". If the SGsAP-IMSI-DETACH-INDICATION message indicated "Combined UE initiated IMSI detach from EPS and non-EPS services", the VLR marks the SGs association as "IMSI detached for EPS and non-EPS services". The VLR shall mark the UE as detached.

If the received MME name is different from the MME name stored in the VLR, the VLR shall not change the state of the SGs association.

5.6 Implicit IMSI detach from non-EPS services p. 33

5.6.1 General description p. 33

This procedure is used by the MME to indicate when, based on the criteria for implicit detach as specified in TS 23.401, the MME has decided to delete the EMM context of an UE or mark its EMM context as detached. This procedure only applies to UEs for which there is an SGs association at the MME.

The implicit IMSI detach from non-EPS services procedure aborts any other ongoing procedure related to this UE on the SGs interface in the MME and in the VLR.

In order to ensure that the VLR and the UE are synchronized as to which paging channel to use for any of the subsequent paging events the MME shall attempt to inform the VLR about the detach event by using a retry scheme if the initial delivery of the SGsAP-IMSI-DETACH-INDICATION message fails.

5.6.2 Procedures in the MME p. 34

When the implicit IMSI detach from non-EPS services procedure is started for a UE, the MME shall send an SGsAP-IMSI-DETACH-INDICATION message to the VLR indicating "Implicit network initiated IMSI detach from EPS and non-EPS services".

After the sending of the SGsAP-IMSI-DETACH-INDICATION message, the MME shall move the state of the SGs association to SGs-NULL. The MME shall start timer Ts10 upon transmission of the SGsAP-IMSI-DETACH-INDICATION message.

If the MME receives an SGsAP-IMSI-DETACH-ACK message from the VLR, the MME shall stop timer Ts10.

If no SGsAP-IMSI-DETACH-ACK message is received by the MME to a previous SGsAP-IMSI-DETACH-INDICATION message before timer Ts10 expires, the MME shall repeat the SGsAP-IMSI-DETACH-INDICATION message a maximum of Ns10 times. The state of the SGs association during the acknowledgement procedure remains SGs-NULL.

5.6.3 Procedures in the VLR p. 34

When a VLR receives the SGsAP-IMSI-DETACH-INDICATION message, the VLR shall send an SGsAP-IMSI-DETACH-ACK message to the sending MME.

The VLR shall check the MME name indicated in the SGsAP-IMSI-DETACH-INDICATION message. If the received MME name is not changed comparing to the MME name stored in the VLR and the state of the SGs association is not SGs-NULL, the VLR proceeds as follows:

The VLR shall move the state of the SGs association for the UE to SGs-NULL. If the VLR does not have a signalling connection for the UE, the VLR shall mark the UE as detached. Additionally, the VLR marks the SGs association as "IMSI implicitly detached for EPS and non-EPS services".

If the received MME name is different from the MME name stored in the VLR, the VLR shall not change the state of the SGs association.

5.7 VLR failure procedure p. 34

5.7.1 General description p. 34

This procedure is used by the VLR to inform the MMEs with an SGs association about the recovery from an internal failure that has affected the SGs association with the MMEs when the VLR fails with restart.

5.7.2 Procedures in the VLR p. 34

5.7.2.1 VLR Reset Initiation p. 34

In the event of a failure at the VLR which has resulted in the loss of the SGs association information for some UEs, the VLR shall move from any state to the SGs-NULL state for these UEs. The VLR shall also set the "Confirmed by Radio Contact" restoration indicator to "false" (see TS 23.007) for affected UEs. The VLR shall not send any SGsAP-MM-INFORMATION-REQUEST messages to UEs with the SGs association in the SGs-NULL state.

When the VLR restarts, the VLR shall send an SGsAP-RESET-INDICATION message to all the MMEs connected to the VLR by the SGs interface. This message indicates to the MME that for the UEs with an SGs association to that VLR, the SGs association is no longer reliable. The VLR shall also start a separate timer Ts11 for each MME.

5.7.2.2 VLR Reset Response p. 34

Upon receipt of an SGsAP-RESET-ACK message from an MME, the VLR shall stop the timer Ts11 for that MME.

5.7.2.3 Abnormal cases p. 35

If the VLR does not receive an SGsAP-RESET-ACK message from that MME before the timer Ts11 expires, the VLR shall retransmit the SGsAP-RESET-INDICATION message. The retransmission is repeated a maximum of Ns11 times.

5.7.3 Procedures in the MME p. 35

5.7.3.1 VLR reset indication p. 35

Upon receipt of an SGsAP-RESET-INDICATION message from the VLR, the MME is informed that all the SGs associations with that VLR for all the UEs registered in the MME are no longer reliable because the VLR has lost information about the state of the UEs and during the failure the VLR might have missed signalling messages. The MME shall set the "VLR-Reliable" MM context variable to "false". The detach procedures for deleting the SGs association are still applicable (see subclause 5.4, subclause 5.5 and subclause 5.6).

The MME sends an SGsAP-RESET-ACK message to the VLR.

If the "VLR-Reliable" MM context variable is set to "false", upon reception of a combined tracking area update request or a periodic tracking area update request from the UE that is attached for non-EPS service, the MME may:

if a combined tracking area update request is received, immediately perform the location update for non-EPS services procedure towards the VLR as described in subclause 5.2; or
if a periodic tracking area update request is received, dependent on network configuration and operator policy,
- perform a network initiated detach with detach type "IMSI detach" immediately after the completion of the periodic tracking area update procedure; or
- perform immediately the location update for non-EPS services procedure towards the VLR as described in subclause 5.2.

5.7.3.2 Void

5.8 MME failure procedure p. 35

5.8.1 General description p. 35

This procedure is used by the MME to inform the associated VLRs about the recovery from an internal failure that has affected the SGs association with the VLRs.

5.8.2 Procedures in the MME p. 35

5.8.2.1 MME Reset Initiation p. 35

In the event of a failure at the MME which has resulted in the loss of the SGs association information on some UEs, the MME shall move from any state to the SGs-NULL state for these affected UEs. The MME shall also set the "MME-Reset" MM context variable to "true" and start the timer Ts12-1. When the timer Ts12-1 expires the "MME-Reset" MM context variable is set to "false".

The MME may send an SGsAP-RESET-INDICATION message to all the VLRs connected to the MME by SGs interfaces. The SGsAP-RESET-INDICATION message indicates to the VLR that all the SGs associations with that particular MME for all the UEs registered in the VLR are no longer reliable. The normal procedures for updating the SGs association are still applicable (see subclause 5.2, subclause 5.4, subclause 5.5 and subclause 5.6). The MME shall also start a separate timer Ts12-2 for each VLR.

If the MME does not send an SGsAP-RESET-INDICATION message, the MME shall move from any state to the SGs-NULL state only for the associations of the UEs affected by the loss of VLR association information.

5.8.2.2 MME Reset Response p. 36

Upon receipt of an SGsAP-RESET-ACK message, the MME shall stop the timer Ts12-2 for that VLR.

5.8.2.3 Abnormal cases p. 36

If the MME does not receive an SGsAP-RESET-ACK message from that VLR before the timer Ts12-2 expires, the MME shall retransmit the SGsAP-RESET-INDICATION message. The retransmission is repeated a maximum of Ns12 times.

5.8.3 Procedures in the VLR p. 36

Upon receipt of an SGsAP-RESET-INDICATION message from the MME, the VLR is informed that all the SGs associations with that MME for all the UEs registered in the MME are no longer reliable because the MME has lost information about the state of the UEs for that VLR and during the failure the MME might have missed signalling messages. The VLR shall either:

set the "Confirmed by Radio Contact" restoration indicator to "false" in all the SGs associations containing the restarted MME and set the state of all the SGs associations containing the restarted MME to the SGs-NULL state; or
keep the 'Confirmed by Radio Contact' restoration indication and the state of all the SGs associations containing the restarted MME unchanged.

The VLR shall then send an SGsAP-RESET-ACK message to the MME.

If the "Confirmed by Radio Contact" restoration indicator is "false" the VLR may send paging messages on both the SGs and the A/Iu interface.

5.9 HSS failure p. 36

5.9.1 General description p. 36

This subclause describes the MME behaviour towards the VLR as a consequence of an HSS reset.

In the case of an HSS failure, the HSS informs the associated MMEs about the recovery from an internal failure that has affected the SGs association with the MMEs according to the HSS reset procedure specified in TS 29.272.

This information is used in the MME to trigger the VLR to perform a location update towards the HSS in order to restore the HSS subscriber data.

5.9.2 Procedures in the MME p. 36

Upon receipt of a HSS reset indication from the HSS, the MME shall set the NEAF for all registered UEs in the MME for which a valid SGs association with a VLR exists.

Upon detection of any signalling activity from the UE, the MME shall report to the VLR if the NEAF, as defined in subclause 5.3.3, is set for this UE. If the MME detects signalling that leads to a procedure towards the VLR, the MME shall follow this procedure and reset the NEAF. If the MME detects activity that does not lead to any procedure towards the VLR, the MME shall send an SGsAP-UE-ACTIVITY-INDICATION message towards the VLR and reset the NEAF. The MME may delay sending the activity indication for a maximum operator-configuration depending time period to avoid high signalling load.