Then the new SGSN informs the HLR of SGSN change, and location information in the HLR database is updated via the MAP protocol on SS7 signaling.
If the HLR receives an indication from an SGSN different from the one stored in its table for a GPRS subscriber, it requests the old SGSN to remove GPRS data related to this subscriber, and then transmits this data to the new SGSN.
This latter then notifies the relevant MS of a GPRS detach.
The network may request the MS to perform a reattach in the case of a network failure condition.
Network-Initiated Combined GPRS Detach When an SGSN wishes to IMSI detach a class A or B MS for GPRS or non-GPRS services, it notifies the relevant MS of a GPRS detach.
When an MS does not need to access GPRS services anymore, an IMSI-detach procedure is initiated, either by the MS or by the SGSN.
During this procedure, the MM context between the MS and the SGSN is removed.