Patent ID: 8441985

Claim:
A method for determining idle mode signaling reduction (ISR) activation in a mobile communications system, the method comprising: (A) receiving, by a first network entity, information on whether IP Multimedia Subsystem (IMS) voice over packet switched (PS) domain is able to be supported, from a second network entity; (B) deciding, by the first network entity, to activate or deactivate an idle mode signaling reduction (ISR) feature based on the information on whether IMS voice over PS domain is able to be supported; and (C) sending, by the first network entity, a context acknowledgement (Ack) message including information on the decision for ISR activation, to the second network entity, wherein the (B) comprises: determining whether the first and second network entities support an ISR feature; determining whether the UE is a UE using IMS voice; and deciding to activate or deactivate the ISR feature according to whether the first and second network entities support IMS voice over PS session.