Content for  TS 29.118  Word version:  18.0.0

The MM information procedure is performed between the VLR and the MME via the SGs interface if the target UE for the MM information procedure is IMSI attached to both EPS and non-EPS services (i.e. the state of the SGs association is SGs-ASSOCIATED). The outcome of the MM Information procedure does not change the state of the SGs association at the VLR or MME.

If for the target UE for the MM information procedure the state of the SGs association in the VLR is SGs-ASSOCIATED, the VLR may initiate the MM information procedure by transferring an SGsAP-MM-INFORMATION-REQUEST message to the MME.

If an SGsAP-MM-INFORMATION-REQUEST message is received for a UE for which there exists an SGs association at the MME, dependent on operator preference the MME shall either:

1. check and update the contents of the received MM information information element. The MME then sends the resultant contents of the MM information information element to the UE indicated in the SGsAP-MM-INFORMATION-REQUEST message, using an EMM INFORMATION message as defined in TS 24.301; or
2. discard the SGsAP-MM-INFORMATION-REQUEST message. In this case the MME can send an EMM INFORMATION message as defined in TS 24.301 to the UE, with contents generated locally by the MME.

The MME should avoid sending both EMM INFORMATION messages according to option 1 and EMM INFORMATION messages according to option 2 to the same UE. For option 1) the MME checks and updates the contents of the MM information information element as follows:

1. If LSA Identity has been included in the MM information, the MME shall discard the LSA Identity;
2. If the network spans more than one time zone, the MME shall handle the time-related parameters as follows:
   • if Network Daylight Saving Time has been included in the MM information, then the MME shall discard the Network Daylight Saving Time;
   • if Local Time Zone has been included in the MM information, then the MME shall replace the Local Time Zone with the Local Time Zone applicable for this UE. In addition, if the local time zone in the MME has been adjusted for daylight saving time, the MME shall indicate this by including the value used for adjustment in Network Daylight Saving Time IE in the MM information;
   • if Universal time and local time zone has been included in the MM information, then the MME shall replace it with the Universal time and local time zone applicable for this UE. In addition, if the local time zone in the MME has been adjusted for daylight saving time, the MME shall indicate this by including the value used for adjustment in Network Daylight Saving Time IE in the MM information;
3. If the network name, i.e. Full name for network or Short name for network or both, has been included by the VLR in the MM information information element, then dependent on operator preference and other information, e.g. the IMSI of the subscriber, the MME may
   • replace the network name received from the VLR with a different network name;
   • remove the network name from the MM information information element; or
   • keep the network name received from the VLR unchanged.

The tunnelling of NAS messages procedure is used to encapsulate the NAS messages exchanged between the UE and the VLR. This procedure can be used by either the VLR or the MME depending on the direction of the NAS message. The two procedures are identified as uplink unitdata, in the direction from the MME to the VLR, and downlink unitdata in the direction from the VLR to the MME.

When the VLR determines that there are no more NAS messages to be exchanged between the VLR and the UE, or when a further exchange of NAS messages for the specified UE is not possible due to an error, the VLR shall send the SGsAP-RELEASE-REQUEST message to the MME, including the IMSI of the UE for which there are no more NAS messages to be tunnelled. Upon receipt of an SGsAP-RELEASE-REQUEST message with an SGs cause information element indicating "IMSI unknown" or "IMSI detached for non-EPS services", the MME shall set the "VLR-Reliable" MM context variable to "false". In addition, the MME requests the UE to re-attach for non-EPS services as specified in TS 24.301.

After the reception of an SGsAP-PAGING-REQUEST message from the VLR, the MME will use this procedure to indicate to the VLR that a NAS signalling connection exists between the UE and the MME. The procedure can be invoked, by the MME as follows:

• Upon reception of a Service Request message or Extended Service Request message from the UE;
• Directly after receiving the SGsAP-PAGING-REQUEST message from the VLR, based on the UE's EMM mode; or
• In Deployment Option 3 (see subclause 8.2.4a.1 of TS 23.272), detecting the UE is temporarily unreachable for paging due to using eDRX (as specified in TS 24.301) and the Service indicator information element in the SGsAP-PAGING-REQUEST message indicates "SMS indicator".

When receiving the SGsAP-PAGING-REQUEST message, the MME shall first take action as described in subclause 5.1.3 and check whether the UE, for which the paging is sent, is in EMM-IDLE or EMM-CONNECTED mode. If the MME accepts the paging request, the MME shall proceed as follows:

• If the UE was in EMM-CONNECTED mode, the MME creates and sends an SGsAP-SERVICE-REQUEST message to the VLR based on the conditions specified in TS 23.272. If the UE subsequently rejects the CS fallback call, the MME shall send the SGsAP-PAGING-REJECT message to the VLR with the SGs cause information element indicating "Mobile terminating CS fallback call rejected by the user";
• If the UE was in EMM-IDLE mode and the SGsAP-PAGING-REQUEST message was received with LAI, the MME shall send the SGsAP-SERVICE-REQUEST message to the VLR when the UE enters EMM-CONNECTED mode;
• If the UE was in EMM-IDLE mode and the SGsAP-PAGING-REQUEST message was received without LAI, the MME behaves as specified in subclause 4.8.1 of TS 23.272; or
• In Deployment Option 3 (see subclause 8.2.4a.1 of TS 23.272), if the UE was in EMM-IDLE mode and temporarily unreachable for paging due to using eDRX (as specified in TS 24.301), and the Service indicator information element in the SGsAP-PAGING-REQUEST message indicates "SMS indicator", the MME behaves as specified in subclause 8.2.4a.3 of TS 23.272.

The MME shall set the service indicator in the SGsAP-SERVICE-REQUEST message equal to what was received in the SGsAP-PAGING-REQUEST message. Additionally, in order to permit the VLR to create an accurate charging record, the MME shall add the IMEISV, the UE Time Zone, the Mobile Station Classmark 2, and the UE's current TAI and E-CGI to the SGsAP-SERVICE-REQUEST message.

Upon reception of the SGsAP-SERVICE-REQUEST message, the VLR shall stop Timer Ts5 and consider the paging procedure as successful. If the paging procedure is for SMS, the VLR shall then start the delivery of the SMS message(s) according to the subclause 5.11.3.1. If the paging procedure with the Service indicator information element indicating "SMS Indicator" was triggered upon reception of a Provide Subscriber Information Request message, the VLR can return an SGs AP-RELEASE-REQUEST message to the MME as specified in subclause 7.2.3.5 of TS 23.018. Other parameters in the message may be used as specified in TS 32.250 and TS 23.078.

This procedure can be invoked by the VLR to abort a mobile terminating CS fallback call during call establishment. The procedure applies to UEs that are simultaneously attached for EPS services and non-EPS services, but not to UEs attached for EPS services and SMS only.

If the VLR decides to abort a mobile terminating CS fallback call for which it has sent an SGsAP-PAGING-REQUEST message to the MME, and the VLR has not received an SCCP connection establishment containing the Initial L3 message from the UE via the A or Iu interface, the VLR shall send the SGsAP-SERVICE-ABORT-REQUEST message to the MME. The state of the SGs association is not changed.

When the MME receives the SGsAP-SERVICE-ABORT-REQUEST message from the VLR, the MME shall set the Call Cancelled Flag to "true". If the MME receives an EXTENDED SERVICE REQUEST message from the UE with Service type set to "mobile terminating CS fallback or 1xCS fallback" and CSFB response set to "CS fallback accepted by the UE" and the Call Cancelled Flag is set to "true", the MME shall set the Call Cancelled Flag to "false" and will reject the CS fallback call as specified in TS 24.301. If the Call Cancelled Flag is set to "true", the MME shall set the Call Cancelled Flag to "false":

• upon reception of the EXTENDED SERVICE REQUEST message from the UE with Service type set to a value other than "mobile terminating CS fallback or 1xCS fallback" or CSFB response set to a value other than "CS fallback accepted by the UE"; or
• upon reception of a new SGsAP-PAGING-REQUEST message from the VLR.

When the MME receives the SGsAP-SERVICE-ABORT-REQUEST message after the UE has accepted the CS fallback call, the MME shall discard the SGsAP-SERVICE-ABORT-REQUEST message. The state of the SGs association is not changed.

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 and the network operating in NMO I and supporting ISR. The implicit 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. 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-EPS-DETACH-INDICATION message fails.

When the implicit IMSI detach from EPS services procedure is started for a UE, the MME shall send an SGsAP-EPS-DETACH-INDICATION message to the VLR indicating "Network initiated IMSI detach from EPS services". After the 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 Ts13 upon transmission of the SGsAP-EPS-DETACH-INDICATION message. If the MME receives an SGsAP-EPS-DETACH-ACK message from the VLR, the MME shall stop timer Ts13. If no SGsAP-EPS-DETACH-ACK message is received by the MME to a previous SGsAP-EPS-DETACH-INDICATION message before timer Ts13 expires, the MME shall repeat the SGsAP-EPS-DETACH-INDICATION message a maximum of Ns10 times. The state of the SGs association during the acknowledgement procedure remains SGs-NULL.

When a VLR receives an SGsAP-EPS-DETACH-INDICATION message, the VLR shall perform the procedures described in subclause 5.4.3.

This procedure is used by the VLR to monitor the status of the UE fallback procedure, after the VLR has sent an SGsAP-PAGING-REQUEST message to the MME.

Upon receipt of an SGsAP-SERVICE-REQUEST message from the MME, if the Service indicator information element in the SGsAP-SERVICE-REQUEST message indicates "CS call indicator", the VLR shall start timer Ts14 to supervise the success of UE fallback. The VLR shall stop timer Ts14 in the following cases:

• upon receipt of an SCCP connection establishment containing the Initial L3 message from the UE via the A or Iu interface;
• upon receipt of an SGsAP-PAGING-REJECT message; or
• upon expiry of the CFNRy timer and if Call Forwarding on No Reply (CFNRy) has been configured and activated for the terminating UE.

If Call Forwarding on No Reply (CFNRy) is not activated for the terminating UE, upon expiry of timer Ts14, the VLR shall release the call as specified in TS 24.008.

If the network is configured to support the return to the last used E-UTRAN PLMN after CS fallback as specified in TS 23.272, this procedure is used to indicate to the VLR that the UE initiated a service request for MO CS fallback.

If the MME is configured to support the return to the last used E-UTRAN PLMN after CS fallback, upon reception of an EXTENDED SERVICE REQUEST message (see TS 24.301) from the UE with Service type set to "mobile originating CS fallback or 1xCS fallback" or "mobile originating CS fallback emergency call or 1xCS fallback emergency call" from the UE, the MME shall send the SGsAP-MO-CSFB-INDICATION message to the VLR.

If the VLR is configured to support the return to the last used E-UTRAN PLMN after CS fallback, upon reception of an SGsAP-MO-CSFB-INDICATION, the VLR shall start timer Ts15 to supervise the success of the UE fallback. If an SCCP connection establishment containing the Initial L3 message is received from the UE via the A or Iu interface, the VLR shall stop timer Ts15 and apply specific handling related to the return to the last used E-UTRAN PLMN after CS fallback. Upon expiry of Ts15, the VLR considers the MO CSFB to have failed and does not apply specific handling related to support of the return to the last used E-UTRAN PLMN after CS fallback.