Design and Implementation of a Distributed Service Invocation Function for the IP Multimedia Subsystem

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Within the standard IMS framework, the value-added service is executed in the Application Server (AS) when the expected event happens. In order to be aware of the event, the AS should be inserted into the SIP signaling path at the beginning of the call to monitor the call progress. As a result, all SIP messages related to the session have to be relayed to the AS to determine whether the service is to be executed or not. However, some services are rarely executed; that is, the procedure of relaying messages to the AS seems unnecessary for most cases of these services. This paper proposes a Distributed Service Invocation Function (DSIF) to eliminate the unnecessary relay.