Patent ID: 7916850

Claim:
A method of controlling subscriber access to SIP-based services facilitated by an IP Multimedia Subsystem, the method comprising: defining at a Serving Call Session Control Function node a default screening trigger applied to all IMS subscribers in a network, wherein said default trigger is applied only to SIP messages of the INVITE type; downloading from a Home Subscriber Subsystem, specific screening triggers allocated to at least certain IMS subscribers; and intercepting at the Serving Call Session Control Function node, at least certain SIP messages originating at subscriber terminals, and for each intercepted message, in the absence of a matching specific screening trigger, activating the default trigger so as to cause the SIP message to be forwarded to a specified SIP application server, wherein the Serving Call Session Control Function node and SIP application server (AS) are located in a home network of the originating subscriber or in a home network of a terminating subscriber.