This TS specifies the stage 1 description of the Immediate Service Termination (IST) service which provides the means for the HPLMN to terminate all the activities of an HPLMN subscriber in a VPLMN.
The purpose of this network feature is to enable the HPLMN to control the activities of its subscribers, particularly while they are roaming. If the HPLMN decides (based upon information received via FIGS or other systems) that a roaming subscriber is behaving in a fraudulent or suspicious manner, the HPLMN can terminate all activities of the subscriber, including calls (including transferred and diverted calls) that are in progress.
This procedure can also be used to terminate all the activities of a subscriber when the subscription has ended.
The primary aim is to enable service providers/network operators to use IST to reduce the amount of money that they lose because of roaming fraud.