03.603GPPGeneral Packet Radio Service (GPRS)Release 1998Service descriptionStage 2TS
The Purge function allows an SGSN to inform the HLR that it has deleted the MM and PDP contexts of a detached MS. The SGSN may, as an implementation option, delete the MM and PDP contexts of an MS immediately after the implicit or explicit detach of the MS. Alternatively, the SGSN may keep for some time the MM and PDP contexts and the authentication triplets of the detached MS, so that the contexts can be reused at a later GPRS attach without accessing the HLR.
When the SGSN deletes the MM and PDP contexts, it shall initiate the Purge procedure as illustrated in Figure 22. Each step is explained in the following list.
Figure 22: Purge Procedure
1) After deleting the MM and PDP contexts of a detached MS, the SGSN sends a Purge MS (IMSI) message to the HLR.
2) The HLR sets the MS Purged for GPRS flag and acknowledges with a Purge MS Ack message.