09.183GPPGeneral Packet Radio Service (GPRS)Gs interface layer 3 specificationServing GPRS Support Node (SGSN) - Visitors Location Register (VLR)TS
10.1 General description
This procedure is used by the SGSN to indicate when an internal SGSN timer mechanism has caused the SGSN to delete the GMM context of an MS or mark its GMM context as detached. This procedure only applies to MSs that are not in the Gs-NULL state at the SGSN.
The implicit 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.
10.2 Procedures in the SGSN
When the implicit IMSI detach from non-GPRS services procedure is started for an MS by the above mentioned internal SGSN timer mechanism, the SGSN shall send a BSSAP+-IMSI-DETACH-INDICATION message to the VLR indicating ‘Implicit SGSN initiated IMSI detach from non-GPRS service’.
After the sending of the BSSAP+-IMSI-DETACH-INDICATION message, the SGSN shall move the state of the association to Gs-NULL. The SGSN shall start timer T10 upon transmission of the BSSAP+-IMSI-DETACH-INDICATION message.
If no BSSAP+-IMSI-DETACH-ACK message is received by the SGSN to a previous BSSAP+-IMSI-DETACH-INDICATION message before timer T10 expires, the SGSN shall repeat the BSSAP+-IMSI-DETACH-INDICATION message a maximum of N10 times. The state of the association during the acknowledgement procedure remains Gs-NULL.
10.3 Procedures in the VLR
When a VLR receives the BSSAP+-IMSI-DETACH-INDICATION message and the state of the association is not Gs-NULL, the state of the association for the MS shall be moved to Gs-NULL. The VLR marks the association as ‘IMSI implicitly detached for GPRS and non-GPRS services’. The VLR shall also send a BSSAP+-IMSI-DETACH-ACK message to the sending SGSN.