4 Information flows

23.0353GPPImmediate Service Termination (IST)Release 17Stage 2TS

4.1 CAMEL implementation

For the Customised Applications for Mobile network Enhanced Logic (CAMEL) implementation of Immediate Service Termination (IST) for a particular subscriber, an "IST" command (in reality, the CAMEL message "ReleaseCall") must be sent by the gsmSCF of the home PLMN to the gsmSSF controlling the call, for all the calls of the subscriber.

Prior to the sending of the IST command, the Mobile Application Part (MAP) command "Cancel Location" should be sent to the VLR at which the subscriber is registered. This will ensure that the subscriber cannot re-commence service at that VLR after the IST command has been executed. See Annex A of TS 22.032 [2].

The compilation of the list of MSCs to which the IST command should be sent is outside the scope of this specification. However, if a PLMN operator wishes to implement IST using CAMEL, the list of MSCs to which the IST command should be sent for a subscriber is the list of MSCs with which the CAMEL server has a relationship for that subscriber. If this data is not available directly from the CAMEL server, it may be obtained using Fraud Information Gathering System (FIGS) or an Fraud Detection System (FDS) (if the HPLMN is using CAMEL for IST then it is likely that it will also be monitoring the subscriber’s activities using FIGS level 2 or 3, which use CAMEL).

4.2 Non-CAMEL implementation

For each non-CAMEL-subscriber under IST control, the HLR shall request the MSCs during location update and routeing information retrieval to report for each remaining activity periodically at the frequency defined by the IST Alert timer value about the remaining activity for this subscriber in the node by sending an IST Alert Message to the HLR, as long as the activity is ongoing. The IST Alert timer value is set by HPLMN and communicated to VPLMN and IPLMN on subscriber basis.

The HLR shall be able to request termination of ongoing call activities for a subscriber by returning a call termination indicator to the MSC in response to the IST Alert message initiated by this MSC. When this call termination indicator is received, the MSC shall terminate the call activities for that subscriber (the MSC shall terminate the call activity that triggered the IST Alert dialogue, and optionally other call activities in that MSC if the MSC is able to link the calls related to the subscriber).

As an implementation option the HLR may for each non-CAMEL-subscriber under IST control maintain a list of MSCs which possibly have ongoing activities for the subscriber. The HLR may then send at any time (i.e. without waiting for the IST Alert message) an unsolicited IST Command message to these MSCs in order to request termination of all ongoing activities for the subscriber. The HLR should send unsolicited IST Command message only to those MSCs that are likely to be carrying a call that needs to be terminated.

Before sending of any IST Command message for a subscriber, the HLR should send the MAP Cancel Location message to the VLR at which the subscriber is registered. This will ensure that the subscriber cannot re-commence service at the corresponding MSC after the IST Command message has been executed. See Annex A of TS 22.032 [2]. The MSC shall be prepared to receive an IST Command message before and/or after the subscriber record has been removed from the VLR.