5 Procedures for SGs

29.1183GPPMobility Management Entity (MME) - Visitor Location Register (VLR) SGs interface specificationRelease 17TS

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

5.1 Paging for non-EPS services procedure

5.1.1 General description

This procedure is used by the VLR to send an SGsAP-PAGING-REQUEST message to a UE. This procedure applies to UEs that are simultaneously attached for EPS services and non-EPS services, or for EPS services and SMS only.

5.1.2 Procedures in the VLR

5.1.2.1 General

The VLR shall handle the timers, queuing and retransmission for sending the SGsAP-PAGING-REQUEST message on the SGs interface in the same way that it handles the sending of a PAGING message on the A or Iu interface.

5.1.2.2 Paging Initiation

When a VLR has to page a UE, the VLR shall check whether the VLR has a SGs association for that UE. The VLR sends SGsAP-PAGING-REQUEST messages to the MME if the MME is in service and the state of the SGs association for the UE is in any of the following states:

– SGs-ASSOCIATED;

– LA-UPDATE-PRESENT or

– SGs-NULL and the "Confirmed by Radio Contact" restoration indicator is set to "false".

If the VLR detects that the MME serving the UE is no longer in service and the VLR supports MT CS services delivery via an alternative MME in the MME pool as defined in 3GPP TS 23.007 [4], the VLR shall send the SGs-PAGING-REQUEST message to one alternative MME in the same MME pool. The VLR shall set the CS restoration indicator in the Additional paging indicators information element.

NOTE 1: The VLR can detect that an MME is no longer in service if there are no SCTP associations in service with that MME.

The sending of the SGsAP-PAGING-REQUEST message does not change the state of the SGs association with the MME.

If the "Confirmed by Radio Contact" restoration indicator is set to "true", the VLR shall include the Location area identifier information element into the SGsAP-PAGING-REQUEST message, otherwise (i.e. after a VLR failure), the VLR shall not include the Location area identifier information element. When sending the SGsAP-PAGING-REQUEST message, the VLR shall start timer Ts5.

If the state of the SGs association is SGs-NULL and the "Confirmed by Radio Contact" restoration indicator is set to "false", the VLR shall also perform a search procedure as specified in 3GPP TS 23.018 [5].

In this message, the VLR includes the Service indicator information element which will be used to indicate the type of CS service. If the SGs paging request is sent as a result of reception of Provide Subscriber Information Request message, the VLR sets the Service indicator information element to either "SMS indicator" or "CS call indicator" as specified in subclause 7.2.3.5 of 3GPP TS 23.018 [5]. For SMS, SMS indicator is used. For all the other CS services, CS call indicator is used.

If the network supports CSFB priority call handling (see 3GPP TS 23.272 [7]) and the call was received with an eMLPP priority level indication (see 3GPP TS 24.008 [8], 3GPP TS 22.067 [24] and 3GPP TS 23.067 [25]), the VLR shall include the value of the received priority level indication in the eMLPP priority information element in the SGsAP-PAGING-REQUEST message.

The eMLPP priority information element may be used to derive the appropriate priority of a SCTP association for the SGsAP-PAGING-REQUEST message.

If the Calling Line Identification of the service (see 3GPP TS 24.081 [12]) is available in the VLR, the VLR may include the CLI information element in the SGsAP-PAGING-REQUEST message. The conditions specified in 3GPP TS 23.081 [5A] and 3GPP TS 29.011 [15A] apply also here.

If the paging is due to a NW-initiated Call Independent SS procedure as defined in 3GPP TS 24.010 [9], the VLR may include the SS code in the SGsAP-PAGING-REQUEST message as defined in 3GPP TS 29.002 [15].

NOTE 2: The SS code used by the VLR does not link to a specific supplementary service. The VLR can use any SS code defined in 3GPP TS 29.002 [15], in the SGsAP-PAGING-REQUEST message.

If the paging is due to a Mobile Terminated Location Request as defined in 3GPP TS 24.030 [11], the VLR shall include LCS indicator in the SGsAP-PAGING-REQUEST message. Additionally, the VLR may include LCS client identity as defined in 3GPP TS 29.002 [15] in the SGsAP-PAGING-REQUEST message.

For Deployment Option 2 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the paging was due to SMS and the SM Delivery Timer and SM Delivery Start Time IEs were received from the SMS-GMSC as defined in 3GPP TS 29.002 [15], the VLR may include these IEs in the SGsAP-PAGING-REQUEST message.

For Deployment Option 2 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the paging was due to SMS and the Maximum Retransmission Time IE was received from the SMS-GMSC as defined in 3GPP TS 29.002 [15], the VLR may include the received Maximum Retransmission Time IE in the SGsAP-PAGING-REQUEST message.

While domain specific access control of the PS domain is ongoing, the VLR shall be configured to send paging messages on both the SGs and the A/Iu interface.

The VLR may apply implementation specific rules for sending the paging on the A/Iu interface. Dependent on network configuration or operator policy, if the UE does not respond to a first paging on SGs interface or the VLR considers UE fallback was failed as described in subclause 5.15.1, and A/Iu paging has not been initiated already, the VLR shall page on the A/Iu interface.

5.1.2.3 Paging Response

The VLR stops the paging procedure towards the MME on expiry of timer Ts5 or on receipt of a SGsAP-SERVICE-REQUEST message from the MME.

On receipt of an SCCP connection establishment containing the Initial L3 message from the UE via the A or Iu interface, the VLR shall stop the paging procedure.

Upon receiving the SGsAP-SERVICE-REQUEST message with the UE EMM mode information element indicating "EMM-CONNECTED", if the Service indicator information element in the SGsAP-SERVICE-REQUEST message indicates "CS call indicator" and Call Forwarding on No Reply (CFNRy) is activated for the subscriber, the VLR shall start the CFNRy timer as specified in 3GPP TS 23.082 [5B].

If the paging response is received via the A or Iu interface from a location area which differs from the one stored in the VLR, the VLR shall move the SGs association to the SGs-NULL state after the UE has been authenticated successfully.

NOTE 2: UE sends this paging response as a result of receiving paging request with IMSI and with CN domain indicator set to "CS" (see 3GPP TS 24.301 [14]).

5.1.2.4 Paging Failure

On receipt of an SGsAP-PAGING-REJECT message before the timer Ts5 expires, the VLR stops timer Ts5. If the SGs cause information element in the SGsAP-PAGING-REJECT message does not indicate "Mobile terminating CS fallback call rejected by the user", the SGs association is moved to the SGs-NULL state and within this state the SGs association is marked with the contents of the SGs cause information element. If the SGs cause information element in the SGsAP-PAGING-REJECT message indicates "IMSI detached for EPS services" the VLR shall send the paging message on the A/Iu interface. If the SGs cause information element indicates "Mobile terminating CS fallback call rejected by the user", the SGs association state shall not be changed.

When the VLR receives the SGsAP-PAGING-REJECT message with the SGs cause information element indicating "Mobile terminating CS fallback call rejected by the user", the VLR shall trigger User Determined User Busy (UDUB) as specified in 3GPP TS 24.082 [13].

5.1.2.5 UE unreachable

On receipt of an SGsAP-UE-UNREACHABLE message before the timer Ts5 expires, the VLR stops timer Ts5, and the paging procedure for that paging request towards the MME is stopped. The state of the SGs association at the VLR is unchanged.

For Deployment Option 2 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the paging was due to SMS and the VLR included the SM-Delivery-Timer and SM-Delivery-Start-Time IEs in the SGsAP-PAGING-REQUEST, and if the SM Buffer Request Indicator bit is set in the Additional UE Unreachable indicators IE in the SGsAP_UE_UNREACHABLE message, the VLR may buffer the Short Message until the time indicated in the SGsAP-PAGING-REQUEST or until receipt of any earlier SGsAP message for the UE.

For Deployment Option 2 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the Retransmission Time IE was included in the SGsAP-UE-UNREACHABLE message, the VLR may forward the received Requested Retransmission Time IE to the SMS-GMSC as defined in 3GPP TS 29.002 [15]. In this case, the VLR shall not set the MNRF flag.

NOTE 1: A/Iu paging can be ongoing.

NOTE 2: If the VLR considers the paging procedure completed, and no response from the UE has been received, and CFNRc has been configured and activated for the terminating UE, the VLR applies the equivalent handling as for Call Forwarding on Not Reachable, as specified in 3GPP TS 23.082 [5B] and 3GPP TS 29.011 [15A].

5.1.3 Procedures in the MME

5.1.3.1 General

The MME accepts SGsAP-PAGING-REQUEST messages in any state of the SGs association. In the SGs-NULL state, the MME accepts SGsAP-PAGING-REQUEST messages only if:

– the "MME-Reset" restoration indicator is set to "true"; or

– the MME supports MT CS services delivery via an alternative MME in the MME pool as defined in 3GPP TS 23.007 [4] and the CS restoration indicator is set in the Additional paging indicators information element in the SGs-PAGING-REQUEST message.

When a MME receives a SGsAP-PAGING-REQUEST message from a VLR, the MME shall first check if the UE is known by the MME. The handling of the paging request depends on the state of the SGs association, the EMM context variables at the MME, and the Service indicator information element in the SGsAP-PAGING-REQUEST message. The MME shall process the paging request and subsequent SGs procedures related to this request preferentially compared to other normal procedures if the SGsAP-PAGING-REQUEST message includes the eMLPP priority information element and if the MME determines the CS call has high priority based on the received value in the eMLPP priority information element (see 3GPP TS 23.272 [7]).

If the Service indicator information element in the SGsAP-PAGING-REQUEST message indicates "CS call indicator", the MME shall handle the paging request as follows:

a) If the UE is known:

– if the UE is considered to be IMSI attached for EPS services and "SMS only", the MME shall return an SGsAP-PAGING-REJECT message to the VLR indicating in the SGs cause information element "Mobile terminating CS fallback call rejected by the user";

– if the UE is considered to be IMSI attached for EPS and non-EPS services (i.e. the SGs association is not in the state SGs-NULL), the MME shall page the UE based on the location information stored in the MME, i.e. in all tracking areas of the stored list. If the SGsAP-PAGING-REQUEST message does not include the Location area identifier information element, the MME may set the "VLR-Reliable" MM context variable to "false". If ISR is activated, and in addition the SGsAP-PAGING-REQUEST message does not include the Location area identifier or the "VLR-Reliable" MM context variable in the MME is set to "false", then the MME shall send Detach Notification (Local Detach) message to the associated SGSN;

– if the MME detects that the UE currently has an ongoing IMS emergency session as specified in subclause 4.6a, 3GPP TS 23.272 [7], the MME shall return an SGsAP-PAGING-REJECT message to the VLR indicating in the SGs cause information element "Mobile terminating CS fallback call rejected by the user";

– if the MME detects that the UE currently has an EPS bearer context with QCI=1 and the MME determines that SRVCC (as specified in 3GPP TS 23.216 [26]) is not supported in the network or it determines that the UE does not support SRVCC, MME shall return SGsAP-PAGING-REJECT message to that VLR with SGs cause information element "Mobile terminating CS fallback call rejected by the user";

– if the UE is marked as IMSI detached for EPS services or IMSI (implicitly or explicitly) detached for non-EPS services (i.e. the state of the SGs association is SGs-NULL):

– if the UE is in the EMM-DEREGISTERED state (see 3GPP TS 24.301 [14]) and if the MME supports MT CS services delivery via an alternative MME in the MME pool and the CS restoration indicator is set in the SGsAP-PAGING-REQUEST message, the MME shall send the paging request with the location information provided by the VLR, regardless of the value of the "MME-Reset" indicator. If no such location information is provided, the MME may either page the UE in all the tracking areas served by that MME or in the tracking areas served by the MME and by the VLR, or reject the paging request per operator policy;

– otherwise, the MME shall return an SGsAP-PAGING-REJECT message to that VLR indicating in the SGs cause information element the detach circumstance ("IMSI detached for EPS services", "IMSI detached for non-EPS services" or "IMSI implicitly detached for non-EPS services");

– if the UE is marked as unreachable, indicated by Paging Proceed Flag set to "false", and the ISR is not activated, the MME shall return an SGsAP-UE-UNREACHABLE message to that VLR indicating in the SGs cause information element "UE unreachable". The state of the SGs association does not change at the MME; or

– if the UE is marked as unreachable, indicated by Paging Proceed Flag set to "false", and the ISR is activated, the MME shall not return an SGsAP-UE-UNREACHABLE message to that VLR. If the SGsAP-PAGING-REQUEST message does not include the Location area identifier or the "VLR-Reliable" MM context variable in the MME is set to "false", then the MME shall send Detach Notification (Local Detach) message to the associated SGSN; Otherwise the MME shall forward the paging request to the associated SGSN, as described in 3GPP TS 29.274 [17A].

b) If the UE is not known and the "MME-Reset" restoration indicator at the MME is set to "false" and if:

– the MME does not support MT CS services delivery via an alternative MME in the MME pool; or

– the MME supports MT CS services delivery via an alternative MME in the MME pool and the CS restoration indicator is not set in the SGsAP-PAGING-REQUEST message;

the MME shall handle the paging request as follows:

– the MME shall return an SGsAP-PAGING-REJECT message to that VLR indicating in the SGs cause information element "IMSI unknown".

c) If the UE is not known and if:

– the "MME-Reset" restoration indicator at the MME is set to "true"; or

– the MME supports MT CS services delivery via an alternative MME in the MME pool and the CS restoration indicator is set in the SGsAP-PAGING-REQUEST message;

the MME shall handle the paging request as follows:

– if the MME only supports "SMS only", the MME shall return an SGsAP-PAGING-REJECT message to the VLR indicating in the SGs cause information element "Mobile terminating CS fallback call rejected by the user";

– if the SGsAP-PAGING-REQUEST message includes the Location area identifier information element, the MME shall page the UE in all the tracking areas served by the MME that can be mapped to the location area indicated in the Location area identifier information element; or

– if the SGsAP-PAGING-REQUEST message does not include the Location area identifier information element, the MME may page in all the tracking areas served by the MME, or the tracking areas served by the MME and by the VLR or reject the paging request per operator policy.

If the Service indicator information element in the SGsAP-PAGING-REQUEST message indicates "SMS indicator", the MME shall handle the paging request as follows:

a) If the UE is known:

– if the UE is considered to be IMSI attached for EPS and non-EPS services or IMSI attached for EPS services and "SMS only", the MME shall page the UE based on the location information stored in the MME. If the SGsAP-PAGING-REQUEST message does not include the Location area identifier information element, the MME may set the "VLR-Reliable" MM context variable to "false". If the UE is using eDRX, the MME may, subject to local operator policy, return an SGsAP-UE-UNREACHABLE message to the VLR indicating in the SGs cause information element "UE temporarily unreachable" while continuing to page the UE. If ISR is activated, and in addition the SGsAP-PAGING-REQUEST message does not include the Location area identifier or the "VLR-Reliable" MM context variable in the MME is set to "false", then the MME shall send Detach Notification (Local Detach) message to the associated SGSN; or

NOTE 2: If location area identifier information element is included in the SGsAP-PAGING-REQUEST, it is not used in paging the UE.

– for Deployment Option 2 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the UE is using eDRX, the SGsAP-PAGING-REQUEST message includes the SM Delivery Timer and SM Delivery Start Time IEs, and the UE is expected to be reachable before the time indicated by the SM-Delivery-Timer and SM-Delivery-Start-Time IEs, the MME may return an SGsAP-UE-UNREACHABLE message to the VLR indicating in the SGs cause information element "UE temporarily unreachable" and setting the SM Buffer Request Indicator bit in the Additional UE Unreachable indicators information element. The state of the SGs association does not change at the MME. The MME should then page the UE when the UE is expected to be reachable.

– for Deployment Option 2 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the UE is using eDRX and the SGsAP-PAGING-REQUEST message includes the Maximum Retransmission Time IEs, the MME may return an SGsAP-UE-UNREACHABLE message to that VLR indicating in the SGs cause information element "UE temporarily unreachable" and including the Requested Retransmission Time IE. In this case, the MME shall set the NEAF. The state of the SGs association does not change at the MME.

NOTE 3: This mechanism does not cause additional signalling at the HLR to retransmit the Short Message.

– if the UE is marked as IMSI detached for EPS services or IMSI (implicitly or explicitly) detached for non-EPS services, or as unreachable, the MME shall proceed as specified for the case when the service indicator indicates "CS call indicator".

b) If the UE is not known and the "MME-Reset" restoration indicator at the MME is set to "false" and if:

– the MME does not support MT CS services delivery via an alternative MME in the MME pool; or

– the MME supports MT CS services delivery via an alternative MME in the MME pool and the CS restoration indicator is not set in the SGsAP-PAGING-REQUEST message;

the MME shall handle the paging request as follows:

– the MME shall return an SGsAP-PAGING-REJECT message to that VLR indicating in the SGs cause information element "IMSI unknown".

c) If the UE is not known and if:

– the "MME-Reset" restoration indicator at the MME is set to "true"; or

– the MME supports MT CS services delivery via an alternative MME in the MME pool and the CS restoration indicator is set in the SGsAP-PAGING-REQUEST message;

the MME shall handle the paging request as follows:

5.1.3.2 Procedure when no NAS signalling connection exists

If the Service indicator information element in the SGsAP-PAGING-REQUEST message indicates "CS call indicator" and the MME accepts the paging request, the MME shall proceed as follows:

– If the SGsAP-PAGING-REQUEST message includes the Location area identifier and the "VLR-Reliable" MM context variable in the MME is set to "true":

– if the UE is considered to be IMSI attached for EPS and non-EPS services, the MME pages the UE with CN domain indicator set to "CS".

– the SGsAP-PAGING-REQUEST message includes the IMSI without TMSI and the location area stored in the MME is the same as the one received in the SGsAP-PAGING-REQUEST message and S-TMSI can be retrieved, and the operator’s policy allows the use of S-TMSI as paging address; or

NOTE: The operator’s policy is related to MSC pool in target RAT.

– the SGsAP-PAGING-REQUEST message includes the TMSI and the location area stored in the MME is the same as the one received in the SGsAP-PAGING-REQUEST message;

then the MME uses the S-TMSI as paging address at the radio interface; else the MME uses the IMSI; and

– if the UE is not known, or is marked as IMSI detached for EPS services or IMSI (implicitly or explicitly) detached for non-EPS services, the MME pages the UE with IMSI and CN domain indicator set to "PS".

– If the SGsAP-PAGING-REQUEST message does not include the Location area identifier, or the "VLR-Reliable" MM context variable in the MME is set to "false":

– if the UE is considered to be IMSI attached for EPS and non-EPS services, the MME uses IMSI as a paging address at the radio interface and CN domain indicator set to "CS". When the MME receives the paging response from the UE, the MME requests the UE to re-attach for non-EPS services as described in 3GPP TS 24.301 [14]; and

– if the UE is not known, or is marked as IMSI detached for EPS services or IMSI (implicitly or explicitly) detached for non-EPS services, the MME pages the UE with IMSI with CN domain indicator set to "PS" to force the UE to re-attach to EPS and non-EPS services as described in 3GPP TS 24.301 [14].

If the Service indicator information element in the SGsAP-PAGING-REQUEST message indicates "SMS indicator" and the MME accepts the paging request, the MME shall proceed as follows:

– If the SGsAP-PAGING-REQUEST message includes the Location area identifier and the "VLR-Reliable" MM context variable in the MME is set to "true":

– if the UE is considered to be IMSI attached for EPS and non-EPS services or IMSI attached for EPS services and "SMS only", the MME shall use the S-TMSI as paging address at the radio interface with CN domain indicator set to "PS". The MME takes action as described in 3GPP TS 24.301 [14], subclause 5.6.2.4; and

– if the UE is not known, or is marked as IMSI detached for EPS services or IMSI (implicitly or explicitly) detached for non-EPS services, the MME pages the UE with IMSI as paging address at the radio interface with CN domain indicator set to "PS". The MME takes action as described in 3GPP TS 24.301 [14], subclause 5.6.2.4.

– If the SGsAP-PAGING-REQUEST message does not include the Location area identifier information element or the "VLR-Reliable" MM context variable is set to "false":

– if the UE is considered to be IMSI attached for EPS and non-EPS services or IMSI attached for EPS services and for "SMS only", the MME uses S-TMSI as paging address at the radio interface with CN domain indicator set to "PS". When the MME receives the paging response from the UE, the MME requests the UE to re-attach for non-EPS services as specified in 3GPP TS 24.301 [14]; and

Independent of the Service indicator information element, if the MME has activated Idle mode Signalling Reduction for the UE, the MME shall forward the paging request to the associated SGSN, as described in 3GPP TS 29.274 [17A].

Independent of the Service indicator information element, the MME shall not retransmit the paging message to the UE. Additionally, if the MME has activated Idle mode Signalling Reduction for the UE, the MME shall not retransmit the paging request to the associated SGSN.

5.1.3.3 Procedure when a NAS signalling connection exists

If the Service indicator information element in the SGsAP-PAGING-REQUEST message indicates "CS call indicator" and the MME accepts the paging request, the MME shall proceed as follows:

– The MME requests the UE to re-attach for non-EPS services as specified in 3GPP TS 24.301 [14] if the SGsAP-PAGING-REQUEST message does not include the Location area identifier, or the "VLR-Reliable" MM context variable in the MME is set to "false"; and

– otherwise, the MME sends the CS SERVICE NOTIFICATION message to the UE through the NAS signalling connection, including the CS service related parameters (CLI, SS code, LCS indicator and LCS client identity), received from the VLR.

If the Service indicator information element in the SGsAP-PAGING-REQUEST message indicates "SMS indicator" and the MME accepts the paging request, the MME shall proceed as follows:

– If the Location area identifier information element is not included in the SGsAP-PAGING-REQUEST message or the "VLR-Reliable" MM context variable is set to "false", the MME requests the UE to re-attach for non-EPS services as specified in 3GPP TS 24.301 [14]; and

– otherwise, the MME need not take any action towards the UE.

5.2 Location update for non-EPS services procedure

5.2.1 General description

The location update for non-EPS services procedure is a general procedure used by UEs which are configured to use CS fallback and SMS over SGs, or SMS over SGs only. This procedure is not performed if:

– the subscriber data indicates that the subscription is for packet only; or

– the MME is registered for SMS for the UE (see 3GPP TS 23.272 [7]).

NOTE: For the cases specified above, the registration with a VLR is not required and the MME does not initiate the location update for non-EPS services procedure.

This procedure allows UEs and the network to perform:

– combined IMSI attach for EPS and non-EPS services or for SMS only;

– IMSI attach for non-EPS services or for SMS only if the UE is already IMSI attached for EPS services;

– normal location update procedure to the VLR if the UE is IMSI attached for both EPS and non-EPS services, or for SMS only; or

– allocation of new TMSI to an UE.

The location update for non-EPS services procedure in the SGs interface is always started as a consequence of a direct action from the UE. The combined attach and tracking area update procedures are further specified in 3GPP TS 23.272 [7] and 3GPP TS 24.301 [14].

When a UE is IMSI attached for EPS and non-EPS services, the VLR shall stop any implicit detach timer. Instead the MME uses the "Paging Proceed Flag" to determine the likely availability of the UE to the network. Upon reception of the periodic Tracking Area Update message, the MME does not report to the VLR, and the MME shall not change the state of the SGs association. When the UE performs a detach only for EPS services or the MME performs an implicit detach for EPS services, and the VLR’s implicit detach timer is not already running, the EPS detach indication to the VLR shall cause the VLR’s implicit detach timer to be restarted from its initial value.

If the MME performs an implicit detach for both EPS and non-EPS services, then the MME shall send to the VLR an SGsAP-IMSI-DETACH-INDICATION message with cause "Implicit network initiated IMSI detach from EPS and non-EPS services", as further described in subclause 5.6 (the implicit IMSI detach message indicates that the UE is unavailable for both EPS and non-EPS services).

5.2.2 Procedures in the MME

5.2.2.1 General

The location update for non-EPS services procedure is initiated with a combined attach or a combined tracking area update procedure. On receipt of an ATTACH REQUEST message or a TRACKING AREA UPDATE REQUEST message from the UE, the MME handles the EPS related request as specified in 3GPP TS 24.301 [14].

When the MME receives the Update Location Answer message containing subscription data from the HSS, the MME determines whether it needs to perform location update for non-EPS services procedure. For the cases identified below, if the MME is configured with ability not to perform registrations with a VLR for the UE, the MME sends response message to the UE without starting the location update for non-EPS services procedure:

– if the Network Access Mode (NAM) subscription data indicates that the subscription is for packet only (see 3GPP TS 29.272 [17]); or

– if the Network Access Mode (NAM) subscription data indicates that the subscription is for packet and circuit (see 3GPP TS 29.272 [17]) and the MME is registered for SMS as specified in annex C of 3GPP TS 23.272 [7] for this UE.

NOTE 1: When the MME supports both SMS in MME feature and SMS over SGs, depending on UE capability and/or network configuration and/or “PS and SMS only” subscription, it can be preferred to provide SMS services via SMS in MME to avoid the VLR registration.

Otherwise, the MME shall start the location update for non-EPS services procedure and shall wait for the outcome of both location update procedures towards the VLR and the HSS before sending the response message to the UE.

NOTE 2: When the combined attach or tracking area update procedure is for both EPS services and non-EPS services and the MME is not registered for SMS for the UE (see 3GPP TS 23.272 [7]) and the UE has "PS and SMS only" subscription, the MME starts the location update for non-EPS services procedure for SMS over SGs only.

5.2.2.2 Location update initiation

5.2.2.2.1 General

If timer Ts6-1 is not running, the MME shall start the location update for non-EPS services procedure when it receives from the UE:

– an attach request indicating combined EPS/IMSI attach;

– a combined tracking area update request indicating Combined TA/LA updating with IMSI attach;

– a combined tracking area update request and the MME detects that the LAI has changed;

– a combined tracking area update request and the state of the SGs association is SGs-NULL; or

– a combined tracking area update request and the MME serving the UE has changed.

If timer Ts6-1 is not running, the MME may start the location update for non-EPS services procedure when it receives from the UE:

– a combined tracking area update request or a periodic tracking area update , if the MM context variable "VLR-Reliable" for the UE is set to "false" (see subclause 5.7.3).

If multiple PLMNs are available for the CS domain, the MME shall select a PLMN for CS domain as specified in 3GPP TS 23.272 [7]. If the MME cannot select any PLMN for CS domain for the UE, the MME informs the UE that the CS domain is not available.

The MME shall determine the new location area identification as follows:

– if the MME received a combined attach request or combined tracking area update request from the UE with an indication for "SMS only", or the network only supports "SMS only" or the network only has a few VLRs that support SGs interface, the MME may allocate a default location area identification specifically configured for that case;

– else the MME derives the location area identification from the current tracking area identity where the UE is located. For this 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 MME shall derive the VLR name from the location area identification which was determined. For networks supporting the feature ‘Intra Domain Connection of RAN Nodes to Multiple CN Nodes’, the VLR name is derived as described in 3GPP TS 23.236 [6A].The MME shall include the location area identification in the new location area identifier information element in the SGsAP-LOCATION-UPDATE-REQUEST message.

NOTE 1: The selection of the VLR in the MME follows the same rule as the selection of the VLR in the SGSN, as defined in 3GPP TS 23.236 [6A].

In networks supporting the feature ‘Intra Domain Connection of RAN Nodes to Multiple CN Nodes’ (3GPP TS 23.236 [6A]), if the TMSI based NRI container is not received from the UE, and the MME determines that the serving VLR of the UE is changed, the MME shall include in the Old location area identifier a specific LAI value which is not broadcasted in the network and not associated with any VLR.

NOTE 2: The MME determines that the serving VLR of the UE is changed when the SGs association changes from one serving VLR to a different one, or based on implementation dependent criteria.

NOTE 3: When the VLR receives the SGsAP-LOCATION-UPDATE-REQUEST message with the specific LAI value, the VLR retrieves the MM context of the UE from the HLR.

In networks supporting the feature "Intra Domain Connection of RAN Nodes to Multiple CN Nodes" as defined in 3GPP TS 23.236 [6A], the MME shall support load re-distribution of UEs to another VLR than the current one. When the MME receives a periodic tracking area update request or a combined tracking area update request, the MME shall check whether for this UE there is a SGs association to a VLR for which load re-distribution has been initiated in the MME by O&M. If this is the case and

– if a combined tracking area update request is received, the MME shall derive the new VLR name as described in 3GPP TS 23.236 [6A] and then send the SGsAP-LOCATION-UPDATE-REQUEST message to the new selected VLR; or

– if a periodic tracking area update request is received, dependent on network configuration and operator policy, the MME shall take one of the following actions:

– perform a network initiated detach with detach type "IMSI detach" immediately after the completion of the periodic tracking area update procedure; or

– derive the new VLR name as described in 3GPP TS 23.236 [6A] and then send the SGsAP-LOCATION-UPDATE-REQUEST message to the new selected VLR.

If the VLR is configured for gateway core network (GWCN), the MME shall select a CS domain operator as specified in 3GPP TS 23.272 [7] and proceed as follows:

– If the preferred RAT of the selected CS domain operator is GERAN and the UE does not support GERAN network sharing (see 3GPP TS 24.008 [8], subclause 10.5.5.12), the MME shall include the selected CS domain operator in the selected CS domain operator information element, and the common PLMN in the new location area identifier information element in the SGsAP-LOCATION-UPDATE-REQUEST message; or

– If only common PLMN ID and no multiple PLMN IDs are provided in CS domain for selection by the UE (see 3GPP TS 23.251 [7A], subclause 4.2.3.1), the MME shall include the selected CS domain operator in the selected CS domain operator information element, and the common PLMN in the new location area identifier information element in the SGsAP-LOCATION-UPDATE-REQUEST message.

If multiple PLMN IDs are provided in CS domain for selection by the UE and the UE supports GERAN network sharing (see 3GPP TS 24.008 [8], subclause 10.5.5.12), the MME shall include the selected PLMN for CS domain in the new location area identifier information element as specified in 3GPP TS 23.251 [7A].

The SGsAP-LOCATION-UPDATE-REQUEST message includes the type of location update performed by the UE in the EPS location update type information element. If the UE has performed a combined attach or a combined tracking area update indicating "combined TA/LA updating with IMSI attach", the MME indicates "IMSI attach", otherwise the MME indicates "Normal location update".

The MME shall include the TMSI status in the SGsAP-LOCATION-UPDATE-REQUEST message if the UE indicates in the ATTACH REQUEST or the TRACKING AREA UPDATE REQUEST message that it has no valid TMSI available. The MME shall also include the old location area identifier in the SGsAP-LOCATION-UPDATE-REQUEST message if the UE included the old location area identification in the ATTACH REQUEST or TRACKING AREA UPDATE REQUEST message.

The MME shall include the TMSI based NRI container in the SGsAP-LOCATION-UPDATE-REQUEST message if received from the UE.

If the MME supports the "Automatic Device Detection" (see 3GPP TS 22.101 [2]) or the "Trace for Management Based Activation/Deactivation" (see 3GPP TS 32.422 [18]), the MME shall include the IMEISV in the SGsAP-LOCATION-UPDATE-REQUEST message.

The MME shall add the UE’s current TAI and E-CGI to the SGsAP-LOCATION-UPDATE-REQUEST message.

When the MME sends the SGsAP-LOCATION-UPDATE-REQUEST, the MME shall start timer Ts6-1.

If timer Ts6-1 is running and the MME receives from the UE:

– an attach request indicating combined EPS/IMSI attach; or

– a combined tracking area update with or without IMSI attach.

Then:

– if the LAI determined by the MME is the same as in the outstanding request, the MME shall not process this new request and shall wait for the VLR response to the ongoing procedure;

– if the LAI determined by the MME is different but the VLR name is the same as for previous LAI, any response from the VLR to the outstanding request is ignored, the MME shall stop and reset timer Ts6-1 and the MME shall start the location update for non-EPS services procedure; or

– if the LAI determined by the MME is different and the VLR name is different as for previous LAI, any response from the previously addressed VLR to the outstanding request is ignored, the MME shall stop and reset timer Ts6-1, and the MME shall start the location update for non-EPS services procedure.

When the MME receives from the UE a tracking area update request and the MME serving the UE has changed, the MME shall stop and reset timer Ts6-1.

5.2.2.2.2 VLR fails without restart

If the MME supports restoration for CS services via an alternative VLR as defined in 3GPP TS 23.007 [4] and, upon reception of a combined tracking area update request or a periodic tracking area update request from the UE, the MME determines that the VLR serving the UE is no longer in service, the MME may:

– if a combined tracking area update request is received, select an alternative VLR that is in service for the UE and immediately perform the location update for non-EPS services procedure towards the selected 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 and then select an alternative VLR that is in service for the UE during the subsequent combined tracking area update procedure, before performing the location update for non-EPS services procedure towards the selected VLR as described in subclause 5.2; or

– select an alternative VLR that is in service for the UE and immediately perform the location update for non-EPS services procedure towards the selected VLR as described in subclause 5.2.

If the MME supports restoration for CS services via an alternative VLR as defined in 3GPP TS 23.007 [4] and, upon reception of an UPLINK NAS TRANSPORT message (see 3GPP TS 24.301 [14]) from the UE, the MME determines that the VLR serving the UE is no longer in service, the MME may:

– request the UE to re-attach for non-EPS services as specified in 3GPP TS 24.301 [14] and then select an alternative VLR that is in service for the UE during the subsequent combined tracking area update procedure, before performing the location update for non-EPS services procedure towards the selected VLR as described in subclause 5.2.

NOTE 1: How an MME detects a VLR is no longer in service and triggers selection of alternative VLR is implemention dependent.

NOTE 2: To avoid large amounts of UEs initiating re-attach for non-EPS services simultaneously, the MME can ignore some MO-SMS. Selection of MO-SMS to ignore is implementation dependent.

5.2.2.3 Location update response

If the MME receives an SGsAP-LOCATION-UPDATE-ACCEPT message from the VLR, the MME shall stop timer Ts6-1 and:

– move the state of the SGs association to SGs-ASSOCIATED;

– set the MM context variable "VLR-Reliable" to "true"; and

– indicate to the UE the acceptance of the VLR to the location update procedure. The message sent to the UE includes the Location Area Identity (see 3GPP TS 24.301 [14]).

The MME shall wait for the outcome of the location update for non-EPS services procedure towards the VLR before sending a response to location update procedure to the UE. When the MME receives an SGsAP-LOCATION-UPDATE-REJECT message from the VLR, it will map the reject cause received to the appropriate reject cause as specified in 3GPP TS 24.301 [14], and report this reject cause to the UE.

If the VLR included the Mobile identity information element in the SGsAP-LOCATION-UPDATE-ACCEPT message, the MME shall relay the information received to the UE. If the Mobile identity information element contains a new TMSI, this will cause the UE to perform a TMSI reallocation procedure. In this case, the MME shall send to the VLR the SGsAP-TMSI-REALLOCATION-COMPLETE message when the MME receives the ATTACH COMPLETE or the TRACKING AREA UPDATE COMPLETE message from the UE. If the Mobile identity information element contains an IMSI, this will cause the UE to deallocate its TMSI.

5.2.2.4 Location update failure

If the MME receives an SGsAP-LOCATION-UPDATE-REJECT message from the VLR, the MME

– shall stop timer Ts6-1;

– shall move the state of the SGs association to SGs-NULL; and

– indicates to the UE the rejection of the Location Update procedure by the VLR as specified in 3GPP TS 24.301 [14]. The Reject cause value sent by the VLR shall be mapped to the appropriate reject cause as specified in 3GPP TS 24.301 [14], and the latter is forwarded to the UE.

NOTE: Upon receiving an SGsAP-LOCATION-UPDATE-REJECT message with MM cause #11 or MM cause #13, if the MME is configured to know that the VPLMN has a suitable roaming agreement for E-UTRAN with the HPLMN of the UE, the MME can map the MM cause to EMM cause #18 as specified in 3GPP TS 24.301 [14].

5.2.2.5 Abnormal cases

If timer Ts6-1 expires, the MME shall abort the Location Update for non-EPS service procedure and indicate this to the UE with the Reject cause value ‘MSC temporarily not reachable’. The state of the SGs association to the VLR shall be SGs-NULL.

If the MME receives an SGsAP-LOCATION-UPDATE-ACCEPT message and timer Ts6-1 is not running then:

– if timer Ts8 is running (see subclause 5.4), the message shall be ignored;

– if timer Ts9 is running (see subclause 5.5), the message shall be ignored; or

– if timers Ts8 and Ts9 are not running:

– if the state of the SGs association to the VLR is SGs-ASSOCIATED, the message shall be ignored; or

– if the state of the SGs association to the VLR is different than SGs-ASSOCIATED, the message shall be treated as a message incompatible with the protocol state of the MME (see subclause 7.3).

5.2.2.6 Additional MME procedure for UE supporting NB-S1 mode only

This subclause applies when the UE supporting NB-S1 mode only requests SMS services via a normal attach request or tracking area update request.

If the UE supporting NB-S1 mode only requests SMS services using normal attach request or tracking area update request, the location update for non-EPS services procedure can be initiated by the MME when SMS over SGs is used.

If timer Ts6-1 is not running, the MME shall start the location update for non-EPS services procedure when it receives from the UE:

– an attach request indicating EPS attach and "SMS only" in NB-S1 mode, SMS services via SMS in MME are not available and SMS over SGs is used for the UE;

– a tracking area update request indicating TA updating and "SMS only" in NB-S1 mode, SMS services via SMS in MME are not available, SMS over SGs is used for the UE and the MME detects that the LAI has changed;

– a tracking area update request indicating TA updating and "SMS only" in NB-S1 mode, SMS services via SMS in MME are not available, SMS over SGs is used for the UE and the state of the SGs association is SGs-NULL; or

NOTE 1: When the MME supports both SMS in MME feature and SMS over SGs, depending on UE capability and/or network configuration and/or "PS and SMS only" subscription, it can be preferred to provide SMS services via SMS in MME to avoid the VLR registration.

NOTE 2: The UE does not include the MS Classmark 2 IE in a normal attach request or normal tracking area update request, and the MME does not store this information or include it in subsequent messages to the VLR. Services that use information part of MS Classmark 2, e.g. CAMEL, can therefore fail when SMS over SGs is provided via normal procedures.

If the MME has a stored TMSI for the UE, the MME may include this TMSI in the TMSI based NRI container IE in the SGsAP-LOCATION-UPDATE-REQUEST message. Otherwise the MME shall indicate "no valid TMSI available" in the TMSI status IE in the SGsAP-LOCATION-UPDATE-REQUEST message.

If the MME received a normal attach request or normal tracking area update request from the UE with an indication for "SMS only", the MME may allocate a default location area identification specifically configured for that case.

If the MME receives an SGsAP-LOCATION-UPDATE-ACCEPT message from the VLR, the MME shall:

– stop timer Ts6-1 and move the state of the SGs association to SGs-ASSOCIATED;

– set the MM context variable "VLR-Reliable" to "true"; and

– indicate to the UE the acceptance of SMS services as specified in 3GPP TS 24.301 [14].

NOTE 3: The message sent to the UE does not include the Location Area Identity or the Mobile identity information element if received from the VLR.

If the VLR included the Location area identifier or the Mobile identity information element in the SGsAP-LOCATION-UPDATE-ACCEPT message, the MME may store the received Location area identifier or the Mobile identity information element for the subsequent location update for non-EPS services procedure for the UE. If the Mobile identity information element contains a new TMSI, the MME may send to the VLR the SGsAP-TMSI-REALLOCATION-COMPLETE message when the MME indicates to the UE the acceptance of SMS services. If the Mobile identity information element contains an IMSI, the MME may delete any stored TMSI for the UE.

If the MME receives an SGsAP-LOCATION-UPDATE-REJECT message from the VLR, the MME shall:

– stop timer Ts6-1 and move the state of the SGs association to SGs-NULL; and

– indicate to the UE the rejection of SMS services as specified in 3GPP TS 24.301 [14]. The MME maps the location update reject cause received from the VLR to an appropriate value as specified in 3GPP TS 24.301 [14] and forwards to the UE.

If timer Ts6-1 expires, the MME shall abort the Location Update for non-EPS service procedure. The MME indicates to the UE the rejection of SMS services by setting an appropriate value and shall as specified in 3GPP TS 24.301 [14] and forwards to the UE. The state of the SGs association to the VLR shall be SGs-NULL.

5.2.3 Procedures in the VLR

5.2.3.1 General

When a VLR receives an SGsAP-LOCATION-UPDATE-REQUEST message, the VLR checks whether the IMSI is known. If the IMSI is not known, the VLR retrieves the MM context of the UE from the HSS.

In networks supporting the feature ‘Intra Domain Connection of RAN Nodes to Multiple CN Nodes’ (3GPP TS 23.236 [6A]), if the TMSI based NRI container is received in the SGsAP-LOCATION-UPDATE-REQUEST message, the VLR derives the NRI value. If the NRI value is not allocated by the VLR, the VLR retrieves the MM context of the UE from the HSS.

When the VLR is configured for gateway core network (GWCN), the VLR shall select the serving CS domain operator as follows:

– If the selected CS domain operator information element is received in the SGsAP-LOCATION-UPDATE-REQUEST message, the VLR shall select the serving CS domain operator as specified in the selected CS domain operator information element;

– If the selected CS domain operator information element is not received in the SGsAP-LOCATION-UPDATE-REQUEST message and the PLMN ID included in the new location area identifier information element identifies a CS domain operator, the VLR shall select the serving CS domain operator as specified in the new location area identifier information element;

– Otherwise, the VLR selects the serving CS domain operator based on local policies.

5.2.3.2 Location update response

If the location update is accepted by the VLR and, if necessary, by the HSS, the VLR shall:

– move the SGs association to the SGs-ASSOCIATED state;

– set the "Confirmed by Radio Contact" restoration indicator to "true";

– update the SGs association by storing the MME address included in SGsAP-LOCATION-UPDATE-REQUEST message; and

– send an SGsAP-LOCATION-UPDATE-ACCEPT message to the sending MME. This message includes the location area identifier received in the New location area identifier information element in the previous SGsAP-LOCATION-UPDATE-REQUEST message.

After the VLR has updated the SGs association, if Ts5 is still running for a MT service for this UE, the VLR shall repeat SGs Paging Request towards the updated SGs association.

5.2.3.3 Location update failure

If the location update is rejected by the VLR, the VLR shall:

– send an SGsAP-LOCATION-UPDATE-REJECT message to the MME with the appropriate reject cause as indicated in 3GPP TS 24.008 [8] and shall indicate to the MME the Location area identifier received in the corresponding SGsAP-LOCATION-UPDATE-REQUEST message; and

– move the SGs association to SGs-NULL.

5.2.3.4 TMSI reallocation procedure

If the VLR decides to allocate a new TMSI to the UE, the VLR shall include the new TMSI in the SGsAP-LOCATION-UPDATE-ACCEPT message. After sending the SGsAP-LOCATION-UPDATE-ACCEPT message with a new TMSI the VLR shall start timer Ts6-2. If the VLR decides to deallocate the TMSI of the UE, the VLR shall include the IMSI of the UE in the SGsAP-LOCATION-UPDATE-ACCEPT message.

Upon receipt of the SGsAP-TMSI-REALLOCATION-COMPLETE message, the VLR shall stop the timer Ts6-2 and consider the new TMSI as valid.

If the IMSI was sent to the UE, the VLR considers the old TMSI if available, as deleted.

If no SGsAP-TMSI-REALLOCATION-COMPLETE message is received by the VLR before the timer Ts6-2 expires, the VLR shall abort the TMSI reallocation procedure. The VLR shall consider the old TMSI if available, occupied until the new TMSI is used in a subsequent A/Iu message, or for an implementation dependent time. The outcome of the TMSI reallocation procedure does not change the state of the SGs association. The VLR uses the IMSI or a TMSI, either the new TMSI or the old TMSI if available, for paging.

NOTE: Whether the new TMSI or old TMSI is used in the SGs paging request does not impact the paging procedure or UE response.

5.2.3.5 Abnormal cases

The following abnormal cases can be identified:

i) MM signalling via A or Iu interface

If the VLR receives a Location Update request or an IMSI detach indication from the UE by the A or Iu interface when the state of the SGs association in the VLR is not SGs-NULL, the VLR shall move the state of the SGs association to SGs-NULL.

ii) Additional Location Update Request

If the state of the SGs association in the VLR is LA-UPDATE PRESENT and an SGsAP-LOCATION-UPDATE-REQUEST message is received, then:

– if the message is from the same MME and indicates the same New location area identifier information element as the outstanding location update request, then the VLR shall ignore this additional SGsAP-LOCATION-UPDATE-REQUEST message;

– if the message is from the same MME but indicates a different New location area identifier information element to the outstanding location update request, then the VLR shall treat this additional SGsAP-LOCATION-UPDATE-REQUEST message and the VLR shall not send any response to the previous SGsAP-LOCATION-UPDATE-REQUEST message; or

– if the message is from a different MME (indicating either the same or different New location area identifier information element) to the outstanding location update request, then the VLR shall treat this additional SGsAP-LOCATION-UPDATE-REQUEST message and the VLR shall not send any response to the previous SGsAP-LOCATION-UPDATE-REQUEST message.

iii) Detach signalling from the MME

If the state of the SGs association in the VLR is LA-UPDATE PRESENT and either an SGsAP-EPS-DETACH-INDICATION or an SGsAP-IMSI-DETACH-INDICATION message is received, then the VLR shall abandon the Location Update for non-EPS services procedure (neither an SGsAP-LOCATION-UPDATE-ACCEPT nor an SGsAP-LOCATION-UPDATE-REJECT messages is sent) and the further actions described in subclauses 5.4 or 5.5 or 5.6 are followed.

iv) Signalling via Gs interface

If the VLR receives for a UE a BSSAP+-LOCATION-UPDATE-REQUEST message (as defined in 3GPP TS 29.018 [16]) from an SGSN when the state of the SGs association for this UE in the VLR is not SGs-NULL, the VLR shall move the state of the SGs association to SGs-NULL.

v) New Location Update Request during TMSI reallocation procedure

If the VLR receives an SGsAP-LOCATION-UPDATE-REQUEST message while Ts6-2 is running, the VLR shall stop timer Ts6-2, abort the TMSI reallocation procedure and proceed with the new location update for non-EPS services procedure. If the VLR needs to page the MS during the new location update for non-EPS services procedure, the VLR uses the IMSI or a TMSI, either the new TMSI from the aborted TMSI reallocation procedure or the old TMSI if available, for paging.

NOTE: Whether the new TMSI or old TMSI is used in the SGs paging request does not impact the paging procedure or UE response.

vi) Reset signalling from the MME

If the state of the SGs association in the VLR is LA-UPDATE PRESENT and an SGsAP-RESET-INDICATION message is received from the MME, then the VLR shall abandon the Location Update for non-EPS services procedure (neither an SGsAP-LOCATION-UPDATE-ACCEPT nor an SGsAP-LOCATION-UPDATE-REJECT messages is sent) and the further actions described in subclause 5.8 are followed.

vii) Collision between A or Iu paging and Location Update Request

If the VLR receives Location Update Request when A or Iu paging is ongoing, then the VLR may abort paging procedure over A or Iu interface and may initiate paging procedure over SGs interface after location updating procedure has successfully completed.

5.3 Non-EPS alert procedure

5.3.1 General description

This procedure is used by the VLR to request from an MME an indication when any signalling activity from the UE is detected. This procedure can be invoked at any time by the VLR. The MME shall acknowledge the SGsAP-ALERT-REQUEST message.

5.3.2 Procedures in the VLR

5.3.2.1 Alert Initiation

The VLR may start the Non-EPS alert procedure at any time. When the VLR wants to request from an MME that further activity from a UE is reported by the MME, the VLR shall send an SGsAP-ALERT-REQUEST message to that MME. The VLR starts timer Ts7 when the SGsAP-ALERT-REQUEST message is sent.

5.3.2.2 Alert Response

When an SGsAP-ALERT-ACK message is received, the VLR shall stop the timer Ts7. The state of the SGs association is not changed.

5.3.2.3 Alert Failure

If an SGsAP-ALERT-REJECT message is received, the VLR shall stop the timer Ts7, move the state of the SGs association to SGs-NULL and within this state the SGs association is marked with the contents of the SGs cause information element.

5.3.2.4 Alert Indication

The VLR shall not change the state of the SGs association upon reception of an SGsAP-UE-ACTIVITY-INDICATION message.

For Deployment Option 2 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the SGsAP-UE-ACTIVITY-INDICATION message includes the Maximum UE Availability Time IE and the MNRF flag is set in the VLR, the VLR may forward the Maximum UE Availability Time IE to the HLR as defined in 3GPP TS 29.002 [15].

5.3.2.5 Abnormal cases

If no SGsAP-ALERT-ACK message is received before the timer Ts7 expires, the VLR shall retransmit the SGsAP-ALERT-REQUEST message a maximum of Ns7 times.

NOTE: If no SGsAP-ALERT-ACK message is received after that, a report is made to the O&M system. The state of the SGs association is not changed.

5.3.3 Procedures in the MME

5.3.3.1 Alert response

The MME may receive an SGsAP-ALERT-REQUEST message in any state of the SGs association. Upon receipt of an SGsAP-ALERT-REQUEST message from the VLR and if the IMSI is known in the MME, the MME shall reply with an SGsAP-ALERT-ACK message and set the NEAF. If the MME has activated Idle mode Signaling Reduction for the UE, the MME shall send an Alert MME Notification message to the associated SGSN, as described in 3GPP TS 29.274 [17A], except for the conditions specified in subclause 8.2.5c of 3GPP TS 23.272 [7].

5.3.3.2 Alert failure

If an SGsAP-ALERT-REQUEST message is received for an IMSI that is unknown at the MME, the MME shall return an SGsAP-ALERT-REJECT message to the VLR indicating the SGs cause information element value "IMSI unknown".

5.3.3.3 Alert indication

The MME shall report to the VLR upon detection of any activity in E-UTRAN (either signalling or, indirectly detected via S-GW, data transfer) from the UE if the NEAF is set. If the MME detects EPS 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. Upon receipt of a UE Activity Notification message from the SGSN, the MME shall reply with a UE Activity Acknowledge message, send an SGsAP-UE-ACTIVITY-INDICATION message to the VLR and reset the NEAF flag.

For Deployment Option 2 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the UE is using eDRX, the MME may include the Maximum UE Availability Time IE in the SGsAP-UE-ACTIVITY-INDICATION message.

NOTE: This information can be used by the SMS Service Center to prioritize the retransmission of pending Mobile Terminated Short Messages to UEs using eDRX.

5.4 Explicit IMSI detach from EPS services

5.4.1 General description

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 3GPP TS 24.301 [14].

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 3GPP TS 24.301 [14], or the MME receives the Detach Notification from the SGSN, as described in 3GPP TS 29.274 [17A], 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 3GPP TS 24.301 [14], 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

5.4.2.1 Explicit EPS detach initiation

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 3GPP TS 24.301 [14];

– 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 3GPP TS 24.301 [14], 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 3GPP TS 24.301 [14], 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

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

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.

NOTE: If no SGsAP-EPS-DETACH-ACK message is received after that, a report is made to the O&M system. The state of the SGs association during the acknowledgement procedure remains SGs-NULL.

5.4.3 Procedures in the VLR

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

5.5.1 General description

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

5.5.2.1 Explicit IMSI detach initiation

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 3GPP TS 29.274 [17A], 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

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

The following abnormal cases can be identified:

i) 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.

ii) 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

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

5.6.1 General description

This procedure is used by the MME to indicate when, based on the criteria for implicit detach as specified in 3GPP TS 23.401 [7B], 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

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

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

5.7.1 General description

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.

NOTE: The VLR recovery procedure is handled in such a way that the signalling load on the VLR and MMEs does not create any overload problem.

5.7.2 Procedures in the VLR

5.7.2.1 VLR Reset Initiation

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 3GPP TS 23.007 [4]) 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

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

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.

NOTE: If no SGsAP-RESET-ACK is received after that a report is made to the O&M system.

5.7.3 Procedures in the MME

5.7.3.1 VLR reset indication

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 subclauses 5.4, 5.5 and 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

5.8.1 General description

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.

NOTE: The MME recovery procedure is handled in such a way that the signalling load on the MME and VLRs does not create any overload problem.

5.8.2 Procedures in the MME

5.8.2.1 MME Reset Initiation

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 subclauses 5.2, 5.4, 5.5 and 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.

NOTE: The option to not send any SGsAP-RESET-INDICATION message to all the VLRs connected to the MME by SGs interfaces reduces subsequent paging signalling initiated by VLRs by avoiding a complete search of the UE on the entire VLR area.

5.8.2.2 MME Reset Response

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

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.

NOTE: If no SGsAP-RESET-ACK is received after that a report is made to the O&M system.

5.8.3 Procedures in the VLR

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.

NOTE: The option to not set the ‘Confirmed by Radio Contact’ restoration indicator to ‘false’ in all the associations containing the restarted MME reduces subsequent paging signalling the VLR can initiate by avoiding a complete search of the UE on the entire VLR area.

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

5.9.1 General description

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 3GPP TS 29.272 [17].

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

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.

5.10 MM information procedure

5.10.1 General description

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.

5.10.2 Procedures in the VLR

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.

5.10.3 Procedures in 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 3GPP TS 24.301 [14]; or

2) discard the SGsAP-MM-INFORMATION-REQUEST message. In this case the MME can send an EMM INFORMATION message as defined in 3GPP TS 24.301 [14] 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.

NOTE 1: Sending messages according to option 1 and option 2 to the same UE can result in short-time changes of the network name or the local time displayed by the UE.

For option 1) the MME checks and updates the contents of the MM information information element as follows:

a) If LSA Identity has been included in the MM information, the MME shall discard the LSA Identity;

b) 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;

NOTE 2: For the determination of the number of time zones, both CS and PS domain are taken into account.

c) 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.

NOTE 3: The network name received from the VLR can be different from the network name provided by the MME, e.g. if multiple PLMNs are available for the CS domain.

5.11 Procedure for tunnelling of NAS messages

5.11.1 General description

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.

5.11.2 Uplink unitdata procedure

5.11.2.1 Procedures in the MME

When the MME receives an Uplink NAS Transport message (see 3GPP TS 24.301 [14]) from a UE, the MME shall copy the value part of the NAS message container information element to the value part of the NAS message container information element of the SGsAP-UPLINK-UNITDATA message and send the SGsAP-UPLINK-UNITDATA message to the VLR if the "VLR-Reliable" MM context variable is not set to "false". If the "VLR-Reliable" MM context variable is set to "false", the MME requests the UE to re-attach for non-EPS services as specified in 3GPP TS 24.301 [14].

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-UPLINK-UNITDATA message.

5.11.2.2 Procedures in the VLR

5.11.2.2.1 General description

Upon reception of an SGsAP-UPLINK-UNITDATA, the VLR shall extract the NAS message container information element and treat the value part of this information element according to the procedures defined in 3GPP TS 24.011 [10].

Other parameters in the message may be used as specified in 3GPP TS 32.250 [17B] and 3GPP TS 23.078 [5AA].

5.11.2.2.2 Abnormal cases

The following abnormal cases can be identified:

i) subscriber data does not exist or is not confirmed by HLR

If the VLR receives an SGsAP-UPLINK-UNITDATA message from the MME for a UE for which subscriber data does not exist or is not confirmed by HLR, then the VLR shall ignore the received message, and return an SGsAP-RELEASE-REQUEST message to the MME with an SGs cause information element indicating "IMSI unknown".

ii) subscriber data exists, but there is no SGs association for the UE at the VLR

If the VLR receives an SGsAP-UPLINK-UNITDATA message from the MME for a UE for which no SGs association exists, then the VLR shall ignore the received message, and return an SGsAP-RELEASE-REQUEST message to the MME with an SGs cause information element indicating "IMSI detached for non-EPS services".

5.11.2.3 Void

5.11.3 Downlink unitdata procedure

5.11.3.1 Procedures in the VLR

When the VLR needs to send a NAS message to the UE, the VLR shall first verify whether or not it has an SGs association for the UE. If the state of the SGs association for the UE is SGs-ASSOCIATED and LA-UPDATE-PRESENT, then the VLR continues with the procedure. The VLR shall build and encapsulate the NAS message into the value part of the NAS message container information element of an SGsAP-DOWNLINK-UNITDATA message and send the SGsAP-DOWNLINK-UNITDATA message to the MME.

5.11.3.2 Procedures in the MME

5.11.3.2.1 General description

Upon reception of an SGsAP-DOWNLINK-UNITDATA message, the MME shall proceed as follows:

– If the UE was in EMM-CONNECTED mode, the MME shall copy the value part of the NAS message container information element to the value part of the NAS message container information element of a Downlink NAS Transport message (see 3GPP TS 24.301 [14]) and shall send the Downlink NAS Transport message to the UE; or

– In Deployment Option 3 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the UE was in EMM-IDLE mode and temporarily unreachable for paging due to using eDRX (as specified in 3GPP TS 24.301 [14]), the MME behaves as specified in subclause 8.2.4a.3 of 3GPP TS 23.272 [7].

5.11.3.2.2 Abnormal cases

The following abnormal cases can be identified:

i) subscriber data does not exist or is not confirmed by HSS

If the MME receives an SGsAP-DOWNLINK-UNITDATA message from the VLR for a UE for which subscriber data does not exist or is not confirmed by HSS, then the MME shall ignore the received message.

ii) subscriber data exists, but there is no SGs association for the UE at the MME

If the MME receives an SGsAP-DOWNLINK-UNITDATA message from the VLR for a UE for which there is no SGs association, then the MME shall ignore the received message.

5.11.3.3 Void

5.11.4 Release procedure

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.

NOTE: For the SMS transport, the VLR can send the SGsAP-RELEASE-REQUEST message when the SMS transaction is complete (reception of a CP-ACK message for the MO case, sending of a CP-ACK message for the MT case), upon reception of a CP-ERROR message, abort of SMS transaction by upper layers, or upon some error cases such as TC1 expiry, no SGs association for the UE or IMSI unknown.

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 3GPP TS 24.301 [14].

5.12 Service request procedure

5.12.1 General description

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 3GPP TS 23.272 [7]), detecting the UE is temporarily unreachable for paging due to using eDRX (as specified in 3GPP TS 24.301 [14]) and the Service indicator information element in the SGsAP-PAGING-REQUEST message indicates "SMS indicator".

5.12.2 Procedures in the MME

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 3GPP TS 23.272 [7]. 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 3GPP TS 23.272 [7]; or

– In Deployment Option 3 (see subclause 8.2.4a.1 of 3GPP TS 23.272 [7]), if the UE was in EMM-IDLE mode and temporarily unreachable for paging due to using eDRX (as specified in 3GPP TS 24.301 [14]), 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 3GPP TS 23.272 [7].

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.

5.12.3 Procedures in the VLR

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 3GPP TS 23.018 [5].

Other parameters in the message may be used as specified in 3GPP TS 32.250 [17B] and 3GPP TS 23.078 [5AA].

5.13 Service abort procedure

5.13.1 General description

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.

5.13.2 Procedures in the VLR

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.

5.13.3 Procedures in the MME

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 3GPP TS 24.301 [14].

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.

5.14 Implicit IMSI detach from EPS services

5.14.1 General description

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.

5.14.2 Procedures in the MME

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.

5.14.3 Procedures in the VLR

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

5.15 UE fallback supervision procedure

5.15.0 General description

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.

5.15.1 Procedures in the VLR

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.

NOTE 1: Upon expiry of the CFNRy timer, the VLR triggers Call Forwarding on No Reply (CFNRy) as specified in 3GPP TS 23.082 [5B] and 3GPP TS 29.011 [15A].

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 3GPP TS 24.008[8].

NOTE 2: Before releasing the call, the VLR needs to consider whether A/Iu paging is ongoing. In addition, if the VLR considers the paging procedure completed, and no response has been received from the UE via the A or Iu interface, and if CFNRc has been configured and activated for the terminating UE, the VLR applies the equivalent handling as for Call Forwarding on Not Reachable, as specified in 3GPP TS 23.082 [5B] and 3GPP TS 29.011 [15A].

5.16 Procedure for MO CSFB indication

5.16.1 General description

If the network is configured to support the return to the last used E-UTRAN PLMN after CS fallback as specified in 3GPP TS 23.272 [7], this procedure is used to indicate to the VLR that the UE initiated a service request for MO CS fallback.

5.16.2 Procedures in the MME

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 3GPP TS 24.301 [14]) 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.

5.16.3 Procedures in 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.