Corporate Convergence with the 3GPP IP Multimedia Subsystem

The future of communications is not only about new and "fancy" services, it also implies the improvement and simplification of day-by-day user experience. In today's mobile networks, there are neither products nor standardized solutions to achieve a functional integration and mobility between a corporate Private Branch Exchange (PBX) based network and a public IP Multimedia Subsystem (IMS) network, e.g. providing value added interworked services from both networks. Some proprietary solutions are based on call forwarding mechanisms and assume two independent subscriptions, and therefore two subscriber numbers. This paper presents some solutions for this problem and proposes an approach based on the "Group registration" which paves the way for a functional integration, starting in a first step with one number service support. The proposed design limits the impact on the PBX installed basis by concentrating the new functionality in the "IMS Gateway". These latter interfaces the corporate domains by means of a User-to-Network interface.