4 Immediate Service Termination (IST)

22.0323GPPImmediate Service Termination (IST)Release 17Service descriptionStage 1TS

4.1 Description

It shall be possible for the Home Public Land Mobile Network (HPLMN) to instruct any PLMN to terminate immediately all the activities of a specified HPLMN subscriber.

Immediate Service Termination (IST) is controlled by the HPLMN and can be triggered by the HPLMN only.

A subscriber shall be specified by the International Mobile Subscriber Identity (IMSI).

For subscribers that are marked as subscribed to a CAMEL-based service, IST shall be possible using Customised Application for Mobile network Enhanced Logic (CAMEL).

IST shall also be possible for subscribers who are not marked as subscribed to any CAMEL-based service (see Annex A).

4.2 Applicability

This network feature applies to all subscribed Bearer Services and Teleservices of the subscriber, except for emergency calls.

4.3 Normal procedure

The HPLMN will normally direct a request for IST for a particular subscriber to the current Visited PLMN (VPLMN) of that subscriber and the PLMN visited by the subscriber immediately prior to visiting the current VPLMN

NOTE: In practice, the IST command will be sent to individual Mobile-services Switching Centres (MSCs), and not to "VPLMNs" as a whole (but such detail is for Stage 2 and not Stage 1). IST will therefore be sent to all MSCs in which the subscriber has (or may have) an active call, as logged by the HPLMN. These MSCs may be confined to the current VPLMN or may include MSC(s) in the PLMN visited by the subscriber immediately prior to visiting the current VPLMN (or PLMNs visited even earlier).

The VPLMN shall confirm receipt of the IST command.

The VPLMN shall then terminate all activities of that subscriber in the VPLMN including ongoing calls and forwarded, deflected and transferred calls. The call records of calls terminated by the operation of IST shall contain a field indicating that the call terminated because of the operation of IST.

The VPLMN shall then confirm to the HPLMN that all subscriber activities in that VPLMN have been terminated.

If the specified subscriber has no activities in the VPLMN then the VPLMN shall inform the HPLMN of this.

4.4 Exception procedures

If after sending an IST command to a VPLMN, the HPLMN does not receive a positive acknowledgement from the VPLMN indicating receipt and comprehension of the IST command, the HPLMN should assume that the VPLMN does not support IST.