19.1.3 Detach IMSI

09.023GPPMobile Application Part (MAP) specificationTS

19.1.3.1 General

On receipt of an A_LU_REQUEST (DETACH IMSI) indication from the radio interface this procedure invokes the MAP_DETACH_IMSI service described in subclause 8.1.5 in order to inform the visitor location register that a subscriber is no longer reachable (see figure 19.1.3/1), e.g. due to switched off station. This information is used by the VLR to reject mobile terminating calls or short messages without sending page messages on the radio path. The service is unconfirmed as it is likely that the MS is switched off before receiving a confirmation.

The detach IMSI feature is optional for the network operator. The MS is informed by the network whether detach IMSI is to be used or not.

+—-+ +—-+ A +—-+ B +—-+
ª MS ª——-ª BS ª—-+——ªMSC ª——-+———ªVLR ª
+—-+ +—-+ +—-+ +—-+
ª ª ªßß
ª A_LU_Request ª ªßß
ª—————————->ª ªßß
ª (DETACH IMSI) ª MAP_DETACH_IMSI ªßß
ª ª———————->ªßß
ª ª ªßß

NOTE: The service shown in dotted lines indicates the trigger provided by the radio interface (see GSM 09.10).

Figure 19.1.3/1: Interface and services for MAP_DETACH_IMSI

If the Gs interface is installed, the procedures to handle an IMSI Detach or a GPRS Detach request from the SGSN via the Gs interface do not require any signalling over the MAP interface. These procedures are specified in GSM 03.60 and 09.18.

19.1.3.2 Detailed procedure in the MSC

The MAP_DETACH_IMSI service is invoked by the MSC when receiving an A_LU_Request (DETACH IMSI) for a subscriber (see figure 19.1.3/2).

The MSC will open the dialogue to the VLR with a MAP_OPEN request containing no user specific parameters. The MAP_DETACH_IMSI request will contain the following parameter received from the radio side (for the mapping see GSM 09.10):

– Subscriber Id, being either a TMSI or an IMSI.

The MSC then waits for the MAP_OPEN confirmation (see macro Receive_Open_Cnf, subclause 25.1), indicating either:

– reject of dialogue (process terminates);

– reversion to version Vr(process terminates); or

– dialogue acceptance.

Thereafter, the dialogue is terminated locally by the MSC (MAP_CLOSE request with Release Method Prearranged End).

19.1.3.3 Detailed procedure in the VLR

When the VLR receives a MAP_DETACH_IMSI indication (see figure 19.1.3/3), it first checks the indication data (macro Check_Indication, see subclause 25.2). Thereafter it is checked whether the subscriber is known:

– if the subscriber is unknown the VLR ignores the indication;

– if the subscriber is known in the VLR, the IMSI detached flag is set.

The VLR process will terminate the dialogue locally (MAP_CLOSE request with Release Method Prearranged End).

Figure 19.1.3/2: Process Detach_IMSI_MSC

Figure 19.1.3/3: Process Detach_IMSI_VLR