Content for TS 23.272 Word version: 17.0.0

1… 4… 5… 5.4… 6… 6.3 6.4… 7… 7.3 7.4… 7.5a… 8… 8.2.4a… 8.3… 8.4… B… B.2… B.2.2… B.2.3a… B.2.3a.4… B.2.4… B.3… C… C.8…

5.4 TA/LA Update procedure 5.4.0 General 5.4.1 Combined TA/LA Update Procedure 5.4.2 Periodic TA and LA Update Procedure 5.4.3 Non-EPS Alert procedure 5.5 Idle Mode Signalling Reduction 5.6 Mobility Management for SMS over SGs only UEs 5.7 Access to CS services after selecting a non-3GPP access
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5.4 TA/LA Update procedure p. 24

5.4.0 General p. 24

When a CS fallback and/or SMS over SGs capable UE is EPS/IMSI attached, it initiates the combined TA/LA procedure based on the triggers specified in TS 23.401.

When a CS fallback and/or SMS over SGs capable UE is not EPS/IMSI attached, it may initiate a combined TA/LA procedure in order to use CS Fallback or SMS over SGs services.

5.4.1 Combined TA/LA Update Procedure p. 24

Copy of original 3GPP image for 3GPP TS 23.272, Fig. 5.4.1-1: Combined TA / LA Update Procedure

Figure 5.4.1-1: Combined TA / LA Update Procedure
(⇒ copy of original 3GPP image)

Step 1.

The UE detects a change to a new TA by discovering that its current TAI is not in the list of TAIs that the UE registered with the network or the UE's TIN indicates the need for a TAU when re-selecting to E-UTRAN. The combined TA/LA Update Procedure is also performed in order to re-establish the SGs association.

A UE that only supports NB-IoT (see TS 23.401) may request SMS service but send a TA Update instead of a combined TA/LA Update.

Step 2.

The UE initiates the TAU procedure by sending a TAU Request (parameters as specified in TS 23.401 including the Update Type, old LAI and Mobile Station Classmark 2) message to the MME. The Update Type indicates that this is a combined Tracking Area/Location Area Update Request or a combined Tracking Area/Location Area Update with IMSI attach Request. If the UE needs SMS service but not CSFB, the UE shall include an "SMS-only" indication in the combined TA/LA Update procedure, see clause 5.6.

Step 3.

Step 4 to step 19 of the EPS TAU procedure are performed as specified in TS 23.401 with the differences as described below when "SMS in MME" applies:

If the MME is enabled to use "SMS in MME" and the MME is not registered with an HSS for that UE (i.e. the MME stores no subscriber data for the UE), the MME performs a registration with HSS as described in Annex C, clause C.8.
If the MME is enabled to use "SMS in MME" and the MME is registered with an HSS for that UE but has no valid SMS subscriber data (i.e. the MME stores subscriber data for the UE but SMS subscriber data have not been requested before or have been removed by the HSS), the MME may perform a re-registration with HSS as described in Annex C, clause C.8 to obtain SMS subscriber data and to provide the HSS with the MME identity to be used for MT-SMS delivery.
If the HSS supports "SMS in MME" the HSS follows the registration procedures described in Annex C, clause C.8.

The MME does not perform any registrations with a VLR, (i.e. it skips steps 4 to 6 and no SGs association is created), if the Network Access Mode information in the subscriber data indicate that the subscription has no CS subscriber data or if the HSS registered the MME for "SMS in MME" for the UE as described in Annex C, clause C.8.

Step 4.

If multiple PLMNs are available for CS domain, the MME performs selection of the PLMN for CS domain and CS domain operator if the selected CS network is shared network configuration, based on current TAI, old LAI and operator selection policies on preferred RAT for CS domain. If the target network is a shared GERAN, the MME shall also take into account the UE capability of support or non-support of GERAN network sharing when selecting the PLMN for the CS domain as specified in TS 23.251. The PLMN selected for CS should be the same that is used for this UE as a target PLMN for PS handovers or for any other mobility procedures related to CSFB. The MME may take any access restrictions provided by the HSS into account, if the network is using separate location areas for GERAN and UTRAN cells. The selected PLMN ID is included in the newly allocated LAI. If the association has to be established or if the LA changed, the new MME sends a Location Update Request (new LAI, IMSI, MME name, Location Update Type, selected CS domain operator) message to the VLR. The cases in which the MME includes the selected CS domain operator towards the VLR are specified in TS 23.251. The MME retrieves the corresponding VLR number from the determined LAI. If multiple MSC/VLRs serve this LAI, the TMSI based NRI as provided by the UE or an IMSI hash function is used to retrieve the VLR number for the LAI as defined in TS 23.236. The Location Update Type shall indicate normal location update. The MME name is a FQDN string.

Step 5.

The VLR performs the normal subscription checks for CS and if all checks are successful performs Location Update procedure in CS domain.

For GWCN configuration, the MSC selects the core network operator as specified in TS 23.251.

Step 6.

The VLR responds with Location Update Accept (VLR TMSI) to the MME.

Step 7.

The MME sends a TAU Accept (parameters as specified in TS 23.401, LAI, VLR TMSI) message to the UE. The VLR TMSI is optional if the VLR has not changed. LAI is determined in step 4 above. The presence of the LAI indicates to the UE that it is IMSI attached. If the UE requests combined TA/LA Update Request without the "SMS-only" indication, and if the network supports SGs for SMS only, the network shall perform the IMSI attach and the MME shall indicate in the TAU Accept message that the IMSI attach is for "SMS-only".

If the UE requests combined TA/LA Update (or combined TA/LA Update with IMSI attach) without the "SMS-only" indication, and if the network supports SGs procedures only for SMS or the network decided to provide "SMS in MME" for the UE, the MME shall indicate "SMS-only" in the TAU Accept message. However, if the network supports CSFB and SMS over SGs and accepts a combined TA/LA Update procedure but does not indicate "SMS-only", the MME may provide a "CSFB Not Preferred" indication to the UE.

If the UE requests combined TA/LA Update (or combined TA/LA Update with IMSI attach) with the "SMS-only" indication, and if the network only supports SGs procedures for SMS or if it supports CSFB and SMS over SGs or if the network decided to provide "SMS in MME" for the UE, the MME shall indicate in the TAU Accept message that the combined TA/LA Update procedure is for "SMS-only".

If the MME provides "SMS in MME" for a UE that requested combined TA/LA Update with IMSI attach, then the TMSI and LAI are provided as specified in clause C.4.2.

The network provides the "SMS-only" or "CSFB Not Preferred" indications based on locally configured operator policies based on e.g. roaming agreement.

The UE behaviour upon receiving such indications is described in TS 23.221.

If the PLMN ID for the CS domain (included in the LAI provided to the UE) differs from the PLMN ID provided as part of the GUTI, the equivalent PLMNs list includes the PLMN ID for the CS domain.

Step 8.

The UE may send a TAU complete message as specified in TS 23.401 for the TAU procedure.

Step 9.

If the VLR has updated the SGs association and if a paging timer is still running for a MT service for this UE, the VLR shall repeat SGs Paging Request towards the updated SGs association.

5.4.2 Periodic TA and LA Update Procedure p. 26

When the UE is camped on E-UTRAN, periodic LA updates shall not be performed, but periodic TA updates shall be performed. In this case, an SGs association is established and the MSC/VLR shall disable implicit detach for EPS-attached UEs and instead rely on the MME to receive periodic TA updates.

When a periodic TA update is not received in the MME, the MME clears the PPF. The lack of periodic TA update may be caused by reselection or handover to GERAN/UTRAN when ISR is active. To ensure CS paging can reach the EPS/IMSI attached UE, the UE shall perform combined RA/LA update in NMO I or LAU in NMO II when the periodic TAU timer expires and the UE is in GERAN/UTRAN (or next returns to coverage in GERAN/UTRAN) and ISR is active.

In addition, when a periodic TA update is not received in the MME, the MME may implicitly detach the UE as specified in TS 23.401. This MME implicit detach does not affect any SGSN attach status. At an implicit detach, the MME also releases the SGs association with the MSC/VLR. The MSC continues to maintain the registered LA for the UE. The MSC changes to supervise LA updates and pages in the still registered LA when mobile terminated services arrive.

When the UE camps on GERAN/UTRAN it may perform combined RA/LA updates. The combined RA/LA update procedures and the conditions for their usage are described in TS 23.060.

5.4.3 Non-EPS Alert procedure p. 26

The MSC/VLR may request an MME to report activity from a specific UE. In this case, the MSC/VLR shall send a SGsAP Alert Request (IMSI) message to the MME where the UE is currently EPS-attached.

Upon reception of the SGsAP Alert Request (IMSI) message, the MME shall set NEAF (Non-EPS Alert Flag). If NEAF is set for an UE, the MME shall inform the MSC/VLR when the next activity from that UE (and the UE is both IMSI- and EPS attached) is detected, and shall clear NEAF.

If the activity detected by the MME leads to a procedure towards the MSC/VLR, the MME shall just follow this procedure. If the activity detected by the MME does not lead to any procedure towards the MSC/VLR, the MME shall send an UE Activity Indication (IMSI) message towards the MSC/VLR.

5.4.4 Void

5.5 Idle Mode Signalling Reduction p. 27

In relation with CSFB and/or SMS over SGs, when ISR is activated, the UE follows regular ISR behaviour. It may reselect between E-UTRAN and GERAN/UTRAN without a need to update the CN. When a mobile terminated service arrives, the MSC/VLR sends a paging message via SGs to the MME. The MME pages in the TA(s) registered for the UE, and, the MME uses the S3 interface to request the SGSN (i.e. the SGSN that has an ISR relation with the MME for that UE) to page the UE in the registered RA. When the UE is already connected with the MME, the MME forwards the paging request only to the UE via the established signalling connection.

When the UE is IMS registered for voice service, even if the UE is configured for CSFB or SMS over SGs, it may need to ignore ISR activation based on the conditions for ISR activation/de-activation for UEs registered for IMS voice service as defined in TS 23.401.

A UE that supports CSFB and/or SMS over SGs includes the "EMM combined procedures capability" indication as part of the "MS Network Capability" in the Attach, RAU or combined RAU/LAU Request message, if the UE supports CSFB service or SMS over SGs. SGSN stores the "EMM combined procedures capability" indication for ISR operation as part of the stored "MS Network Capability". If the UE does not support CSFB or SMS over SGs, it shall not include the "EMM combined procedures capability" indication in the Attach, RAU or combined RAU/LAU Request message to SGSN.

ISR remains activated until the UE performs a combined RAU/LAU procedure (e.g. a UE in NMO I moves to a new RA or LA or the periodic TAU timer expires while the UE is in NMO I of GERAN/UTRAN) or separate LAU procedure (e.g. a UE moves to a different LA in NMO II or the periodic TAU timer expires while the UE is in NMO II of GERAN/UTRAN). Normal re-selection between registered RA/TA(s) does not cause ISR deactivated condition. When the UE needs to perform a combined RAU/LAU, the SGSN checks the "EMM combined procedures capability" bit in MS Network Capability and if it indicates that CSFB and/or SMS over SGs is supported then the SGSN deactivates ISR by not indicating ISR activated in the combined RAU Accept message, which is a regular ISR functionality as specified in TS 23.401. So an SGSN in a CSFB/SMS over SGs configuration never indicates ISR activated in combined RAU procedures for a UE that supports CSFB/SMS over SGs. An SGSN with ISR capability in a CSFB/SMS over SGs configuration shall always maintain ISR by indicating ISR Activated in Periodic RAU Accept for a UE that supports CSFB/SMS over SGs if the SGSN has the status that ISR is activated for the UE. After a combined RA/LA update procedure, the MSC pages via Gs for mobile terminated services. When Gs is not used, the MSC/VLR pages in the LA via Iu/A for mobile terminated services.

If ISR is deactivated and the UE re-selects to E-UTRAN with the TIN indicating "P-TMSI", it initiates a TAU procedure, which is a regular ISR functionality as specified in TS 23.401, and ISR can be activated again. The UE that supports CS fallback/SMS over SGs shall perform this TAU procedure as a combined TA/LA Update Procedure.

In case of the detach procedure for E-UTRAN when ISR is activated, the MME notifies the associated SGSN with indicating detach cause (i.e. local detach or complete detach) as specified in clause 5.3.1, 5.3.2, 5.3.3 and TS 23.401 except UE-initiated IMSI detach only procedure.

In case of the detach procedure for GERAN/UTRAN when ISR is activated, the SGSN sends an IMSI or GRPS Detach indication message to the VLR depending on the detach type sent by the UE as specified in clause 6.6.1 of TS 23.060, and notifies the associated MME with indicating detach cause (i.e. local detach, complete detach or IMSI detach only) and detach type (i.e. PS detach or combined PS/CS detach) in case of complete detach, and the MME sends IMSI Detach Indication or EPS Detach Indication message to the MSC/VLR accordingly, which is specified in clause 5.3.1A and 5.3.2A.

When the MME receives a SGs paging for CS service, if ISR is activated and the mobile reachable timer has expired but the Implicit Detach timer has not expired, the MME shall not notify the MSC/VLR that the UE is unreachable via SGs and instead shall page the UE via S3 interface.

When implicit detach timer expires in the MME, the MME shall send EPS Detach Indication message. .

The SGSN in NMO I configuration with ISR capability shall support the "EMM combined UE Waiting Flag". The "EMM Combined UE Waiting Flag" shall be turned on if SGSN sends Detach Request (IMSI Detach) to the UE as specified in clause 5.3.2.

If "EMM Combined UE Waiting Flag" is turned on in the SGSN, then the SGSN shall behave as follows:

If the SGSN receives Periodic RAU from the UE, the SGSN shall send Detach Request (IMSI Detach) to the UE.
If the SGSN receives Combined RAU from the UE, the SGSN shall continue the procedure as specified in TS 23.060.
If the SGSN receives Service Request from the UE, the SGSN handles the Service Request normally and shall send Detach Request (IMSI Detach) to the UE.
The SGSN shall turn off the "EMM Combined UE Waiting Flag" if the SGSN receives Combined RAU from the UE.

The MME may activate ISR if "SMS in MME" for the UE is used.

For PS-only Service Provision per clause 5.3.18 of TS 23.060 if SGSN provides SMS services via PS domain for a UE, the SGSN may activate ISR for this UE by indicating ISR Activated in Combined RAU Accept message.

5.6 Mobility Management for SMS over SGs only UEs p. 28

UEs that need SMS service but not CSFB indicate this specific condition with the "SMS-only" indication in the EPS/IMSI Attach Request and combined TA/LA update procedures (or, for a UE that only supports NB-IoT, optionally using the EPS Attach Request and TA update procedures, see TS 23.401). This allows an operator to deploy the SGs for SMS delivery over LTE only without the need for CSFB support. In addition, this allows the MME to use a dedicated algorithm for the selection of the MSC that supports those UEs. An MME that supports "SMS in MME" may directly handle SMS services for the UE under the conditions described in clause C.4.2.

5.7 Access to CS services after selecting a non-3GPP access |R11| p. 28

When a UE, which obtained voice and/or SMS services using an EPS/IMSI registration via E-UTRAN, selects a non-3GPP access network, the UE tries to retain these services by actions described in clause 7.2a of TS 23.221.