9 Explicit IMSI detach from non-GPRS services procedure

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

9.1 General description

This procedure is used by the SGSN to indicate to the VLR that the MS has performed IMSI detach from non-GPRS services and therefore the association between the SGSN and the VLR has to be deactivated. This procedure only applies to MSs that are not in the Gs-NULL state at the SGSN . The procedures specified in this section only apply to IMSI detach or combined IMSI and GPRS detach requests.

The explicit IMSI detach from non-GPRS services procedure aborts any other ongoing procedure related to this MS on the Gs interface in the SGSN and in the VLR.

The VLR and the MS should be synchronised as to whether the PBCCH or the BCCH is used, for any of the subsequent paging.. In order to achieve this, the SGSN shall attempt to inform the VLR about the detach event by using a retry scheme if the initial delivery of the BSSAP+-IMSI-DETACH-INDICATION message fails.

9.2 Procedures in the SGSN

9.2.1 Explicit IMSI detach initiation

When an SGSN receives a Detach Request from an MS which is not in the Gs-NULL state, it shall check the detach type indicated. If the MS is indicating IMSI detach or combined IMSI and GPRS detach the SGSN shall send an BSSAP+-IMSI-DETACH-INDICATION message to the VLR indicating ‘Explicit MS initiated IMSI detach from non-GPRS service’ or ‘Combined explicit MS initiated IMSI detach from GPRS and non-GPRS services’.

After the sending of the BSSAP+-IMSI-DETACH-INDICATION message to the VLR, the SGSN shall move the state of the association to Gs-NULL. The SGSN shall start timer T9 upon transmission of the BSSAP+-IMSI-DETACH-INDICATION message and if timer T6-1 is running, timer T6-1 shall be stopped and reset..

9.2.2 Explicit IMSI detach Response

If the detach type received from the MS indicated IMSI only detach or combined IMSI and GPRS detach not due to switch off, the SGSN shall wait for the reception of the BSSAP+-IMSI-DETACH-ACK message before sending the confirmation of the detach to the MS.

9.2.3 Abnormal cases

i) with switch off

If the SGSN sent a BSSAP+-IMSI-DETACH-INDICATION message for a combined IMSI and GPRS detach due to switch off and timer T9 expires, the SGSN shall repeat the BSSAP+-IMSI-DETACH-INDICATION message a maximum of N9 times.

ii) with no switch off

If the SGSN sent a BSSAP+-IMSI-DETACH-INDICATION message for a IMSI only detach or a combined IMSI and GPRS detach not due to switch off and timer T9 expires, the SGSN shall repeat the BSSAP+-IMSI-DETACH-INDICATION message a maximum of N9 times. If no BSSAP+-IMSI-DETACH-ACK is received after that the SGSN shall send the confirmation of the detach to the MS.

9.3 Procedures in the VLR

When a VLR receives an BSSAP+-IMSI-DETACH-INDICATION message , the VLR shall send an BSSAP+-IMSI-DETACH-ACK message to the sending SGSN. The state of the association for the MS shall be moved from any state to Gs-NULL. If the BSSAP+-IMSI-DETACH-INDICATION message indicated ‘Explicit MS initiated IMSI detach from non-GPRS service’, the VLR marks the association as ‘IMSI detached for non-GPRS services’. If the BSSAP+-IMSI-DETACH-INDICATION message indicated ‘Combined explicit MS initiated IMSI detach from GPRS and non-GPRS services’, the VLR marks the association as ‘IMSI detached for GPRS and non-GPRS services’.