Edward Alan Clark

Dual mode service: Learning from integrating an IP multimedia subsystem service into existing live networks

The IP Multimedia Subsystem (IMS) is an open, standards-based solution for delivering advanced communications services over IP networks. One such service is the dual mode service (DMS), that allows a subscriber to roam across multiple access networks, including Wi-Fi and macro-cellular, using a dual mode handset (DMH). In addition, fixed residential and enterprise numbers receive telephony services through Voice over Internet Protocol (VoIP). The service includes the ability to simultaneously ring multiple endpoints, ring them distinctively for different called numbers, and view logs of all calls. Several deployable architecture options are possible for building DMS, ranging from legacy, circuit switched network solutions through next-generation network solutions using an IMS architecture. Integrating new services and network elements is typically a time consuming and costly endeavor. In this paper, we report our experiences designing, integrating, and deploying a carrier-grade DMS based on an IMS architecture that overcomes many limitations found in other solutions. Our experience with DMS shows that cost and service development time is reduced by leveraging the IMS cores scalability, failover mechanisms, and service provisioning, rather than recreating all these mechanisms in service-specific platforms.