6 Location Update for non-GPRS services procedure

09.183GPPGeneral Packet Radio Service (GPRS)Gs interface layer 3 specificationServing GPRS Support Node (SGSN) - Visitors Location Register (VLR)TS

6.1 General description

The location update for non-GPRS services procedure is a general procedure used by MSs in class-A mode of operation and MSs in class-B mode of operation. This procedure allows MSs and network to perform:

– Combined IMSI attach for GPRS and non-GPRS services.

– IMSI attach for non-GPRS services if the MS is already IMSI attached for GPRS services.

– IMSI attach for GPRS services indication to the VLR if the MS is already IMSI attached for non-GPRS services

– Normal Location Update procedure to the VLR if the MS is IMSI attached for both GPRS and non-GPRS services.

– Reallocation of TMSI to an MS.

The Location Update for non-GPRS services procedures in the Gs interface is always started as a consequence of a direct action by the MS. The combined routeing area update procedure is further specified in 3GPP TS 03.60 and 04.08.

The Location Update for non-GPRS services procedure is used by the SGSN to forward to the VLR those parts of the combined routeing area update or IMSI attach procedure which belong to the non-GPRS services. This means that non-GPRS related requests which are included in the combined request, are sent from the SGSN to the VLR. The procedure is also used by the SGSN to indicate to the VLR when an IMSI attach to GPRS services has been performed by an MS that was already IMSI attached to non-GPRS services. The SGSN may also forward a BSSAP+-TMSI-REALLOCATION-COMPLETE message from the MS to the VLR.

The VLR shall acknowledge the BSSAP+-LOCATION-UPDATE-REQUEST message. When the VLR processes the request it does not perform authentication because it relies on the SGSN’s security functions.

When an MS is IMSI attached for GPRS and non-GPRS services, any implicit detach timer in the VLR shall be stopped. Instead the Paging Proceed Flag in the SGSN is used to determine the likely availability of the MS to the network. Upon reception of the periodic Routeing Area Update message the SGSN does not report to the VLR, and the state of the association at the SGSN is not changed. When the MS performs a detach only from the GPRS system the GPRS detach indication to the VLR shall cause the VLR’s implicit detach timer to be restarted from its initial value.

If the SGSN performs an implicit detach for both GPRS and non-GPRS traffic, then the SGSN shall indicate to the VLR a BSSAP+-IMSI-DETACH-INDICATION message with cause ‘Implicit SGSN initiated IMSI detach from non-GPRS service’, as further described in section ‘Implicit IMSI detach from non-GPRS service procedure’ (the implicit IMSI detach message indicates that the MS is unavailable for both GPRS and non-GPRS services).

The IMSI attach for GPRS services to the VLR, when the MS is already IMSI attached for non-GPRS services, is requested by the MS sending a combined IMSI attach for GPRS and non-GPRS services message to the SGSN, as further specified in 3GPP TS 03.60 and 04.08.

6.2 Procedures in the SGSN

The Location Update for non-GPRS services is initiated with a routeing area update procedure or a IMSI/GPRS attach procedure. On receipt of a Routeing Area Update message, the SGSN shall handle the GPRS related request as specified in 3GPP TS 04.08. The Location Update for non-GPRS services procedure may be handled by the SGSN in parallel to the Update Location procedure to the HLR. The SGSN shall wait for the outcome of both location update procedures towards the VLR and the HLR before sending the response message to the MS (see 3GPP TS 04.08).

6.2.1 Location Update Initiation

If timer T6-1 is not running, the SGSN shall start the Location Update for non-GPRS service procedure when it receives from the MS:

– An Attach request indicating combined IMSI and GPRS attach ;

– An Attach request indicating IMSI only attach ;

– A Routeing Area Update request indicating that the Location Area has changed ; or

– A Routeing Area Update request when the SGSN serving the MS has changed.

The number of the VLR is derived from the RAI where the MS is camping. The SGSN starts Timer T6-1. The BSSAP+-LOCATION-UPDATE-REQUEST message includes the old Location Area Identifier received from the MS. The SGSN shall also include the new Location Area Identifier where the MS is currently camping. The new LAI is derived from the RAI.

The BSSAP+-LOCATION-UPDATE-REQUEST message includes the type of location update performed by the MS in the GPRS location update type IE. If the MS has performed an attach request, the SGSN indicates ‘IMSI attach’, otherwise the SGSN indicates ‘Normal location update’.

The BSSAP+-LOCATION-UPDATE-REQUEST message shall include the TMSI status if received from the MS.

If timer T6-1 is running:

If the SGSN receives from the MS:

– An Attach request indicating combined IMSI and GPRS attach ;

– An Attach request indicating IMSI only attach ; or

– A Routeing Area Update request indicating that the Location Area has changed.

Then:

– If the new LAI is the same as in the outstanding request, the SGSN shall not process this new request and shall wait for the VLR’s response to the ongoing procedure ; or

– If the new LAI is different but is in the same VLR as the outstanding request:

– any response from the VLR to the oustanding request is ignored ;

– Timer T6-1 shall stopped and reset ; and

– The SGSN shall start the Location Update for non-GPRS service procedure ; or

– If the new LAI is different, and is in a different VLR to the outstanding request:

– Any response from the previously addressed VLR to the oustanding request is ignored ;

– Timer T6-1 shall stopped and reset ; and

– the SGSN shall start the Location Update for non-GPRS service procedure.

When the SGSN receives from the MS a Routeing Area Update request and the SGSN serving the MS has changed, the SGSN shall stop and reset timer T6-1.

6.2.2 Location Update Response

If the SGSN receives a BSSAP+-LOCATION-UPDATE-ACCEPT message from the VLR, the SGSN shall:

stop timer T6-1 and

– Move the state of the association to Gs-ASSOCIATED ;

– Set the the MM context variable ‘VLR-Reliable’ to ‘true’ ; and

– Indicate to the MS the acceptance of the VLR to the Location Update procedure. The message to the MS includes the Routeing Area Identity, from which the MS is able to extract the location area identity for which the location update procedure succeeded (see 3GPP TS 04.08).

The SGSN shall wait for the outcome of the Location Update for non-GPRS service procedure towards the VLR before sending a response to location update procedure to the MS. Any Reject cause that needs to be reported to the MS is specified in 3GPP TS 04.08.

If the VLR included the Mobile Identity IE in the BSSAP+-LOCATION-UPDATE-ACCEPT message, the SGSN shall forward the information received to the MS. If the Mobile Identity IE contains a new TMSI it will cause the MS to perform a TMSI reallocation procedure, while an IMSI causes the MS to deallocate its TMSI. In case a new TMSI was allocated for the MS the SGSN shall send to the VLR the BSSAP+-TMSI-REALLOCATION-COMPLETE message when the SGSN receives the Attach Complete or the Routeing Area Complete message from the MS.

6.2.3 Location Update Failure

If the SGSN receives a BSSAP+-LOCATION-UPDATE-REJECT message from the VLR, the SGSN shall:

– Stop timer T6-1;

– Move the state of the association to Gs-NULL; and

– Indicate to the MS the rejection of the VLR of the Location Update procedure as specified in 3GPP TS 04.08. The Reject cause value sent by the VLR shall be forwarded to the MS.

6.2.4 Abnormal cases

If timer T6-1 expires, the SGSN shall abort the Location Update for non-GPRS service procedure and indicate this to the MS with the Reject cause value ‘MSC temporarily not reachable’. The state of the association to the VLR shall be Gs-NULL.

If the SGSN receives a BSSAP+LOCATION-UPDATE-ACCEPT message and timer T6-1 is not running then:

– If timer T8 is running (see section 8), the message shall be ignored;

– If timer T9 is running (see section 9), the message shall be ignored; or

– If timers T8 and T9 are not running:

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

– If the state of the association to the VLR is different than GS-ASSOCIATED, the message shall be treated as a message incompatible with the protocol state of the SGSN (see section 16.3).

6.3 Procedures in the VLR

When a VLR receives a BSSAP+-LOCATION-UPDATE-REQUEST message it shall check whether the IMSI is known. If the IMSI is not known the VLR shall retrieve the MM context of the MS from the HLR.

6.3.1 Location Update Response

If the Location Update is accepted by the VLR and, if necessary by the HLR, the VLR shall:

– Move the association to the Gs-ASSOCIATED state ;

– Set the restoration indicator ‘Confirmed by Radio Contact’ to ‘true’ ;

– Update the association by storing the SGSN number included in the BSSAP+-LOCATION-UPDATE-REQUEST message ; and

– Send a BSSAP+-LOCATION-UPDATE-ACCEPT message to the sending SGSN. This message includes the Location Area Identification received in the new Location Area Identification IE in the previous BSSAP+-LOCATION-UPDATE-REQUEST message.

6.3.2 Location Update Failure

If the Location Update is rejected by the VLR it shall:

– Send a BSSAP+-LOCATION-UPDATE-REJECT message to the SGSN with the appropriate reject cause as indicated in 3GPP TS 04.08; and

– Move the association from any state to Gs-NULL.

6.3.3 TMSI reallocation procedure

If the VLR decides to reallocate the TMSI to the MS it shall include the new TMSI in the BSSAP+-LOCATION-UPDATE-ACCEPT message. If the VLR decides to deallocate the TMSI of the MS it shall include the IMSI of the MS in the BSSAP+-LOCATION-UPDATE-ACCEPT message. After sending the BSSAP+-LOCATION-UPDATE-ACCEPT message with a new TMSI the VLR starts timer T6-2.NOTE: In the BSSAP+-LOCATION-UPDATE-REQUEST the SGSN may indicate, that there is no valid TMSI available in the MS. This information may be used by the VLR to decide whether to reallocate a new TMSI to the MS.

Upon receipt of the BSSAP+-TMSI-REALLOCATION-COMPLETE message, the VLR stops the timer T6-2 and considers the new TMSI as valid.I

If an IMSI was sent to the MS, the VLR considers the old TMSI as deleted.

If no BSSAP+-TMSI-REALLOCATION-COMPLETE message is received by the VLR before the timer T6-2 expires, the VLR aborts the TMSI reallocation procedure. The VLR may still perform the TMSI reallocation procedure via the A interface. The outcome of the TMSI reallocation procedure does not change the state of the association. The VLR uses the IMSI or the new TMSI for paging.

6.3.4 Abnormal cases

i) MM signalling via A interface

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

ii) Additional Location Update Request

If the state of the association in the VLR is in the LA-UPDATE PRESENT state and a BSSAP+-LOCATION-UPDATE-REQUEST message is received, then:

– If the message is from the same SGSN and indicates the same New Location Area as the outstanding location update request, then this additional BSSAP+-LOCATION-UPDATE-REQUEST message shall be ignored ;

– If the message is from the same SGSN but indicates a different New Location Area to the outstanding location update request, then this additional BSSAP+-LOCATION-UPDATE-REQUEST message shall be treated and the VLR shall not send any response to the previous BSSAP+-LOCATION-UPDATE-REQUEST message ; or

– If the message is from a different SGSN (indicating either the same or different New Location Area) to the outstanding location update request, then this additional BSSAP+-LOCATION-UPDATE-REQUEST message shall be treated and the VLR shall not send any response to the previous BSSAP+-LOCATION-UPDATE-REQUEST message.

iii) Detach signalling from SGSN

If the state of the association in the VLR is in the LA-UPDATE PRESENT state and either a BSSAP+-GPRS-DETACH-INDICATION or a BSSAP+-IMSI-DETACH-INDICATION message is received, then, the Location Update for non-GPRS services procedure shall be abandoned in the VLR (neither a BSSAP+LOCATION-UPDATE-ACCEPT nor a BSSAP+LOCATION-UPDATE-REJECT messages is sent) and the further actions described in sections 8 or 9 or 10 are followed.