System and method for call completion on busy subscribers

摘要

The invention relates to a system and methods for allowing the extension of the ISDN/GSM Call Completion to Busy Subscriber Supplementary Service across a Network Boundary between a general Switched Circuit Network (SCN) using ISUP as call control protocol, and an IP Packet Network using SIP as session control protocol. The methods define the set of new protocol elements to be included or amended in the Session Initiation Protocol (SIP) in order to make it possible the implementation of the required service logic in SIP User Agents and Clients. Apart from the aforementioned protocol extensions, the methods define the set of sequences, timers and use cases that a so-called Network Gateway must fulfil in order to allow users from both networks to invoke the service for calls going through the Network Gateway in question. Specifically, said Network Gateway represents an end-point for both SCN and SIP domains.