An open (in the sense of extensible and programmable) architecture for IP telecommunications must be based on a comprehensive strategy for managing feature interaction. We describe our experience with BoxOS, an IP telecommunication platform that implements the DFC technology for feature composition. We present solutions to problems, common to all efforts in IP telecommunications, of feature distribution, interoperability, and media management. We also explain how BoxOS addresses many deficiencies in SIP, including how BoxOS can be used as a SIP application server.

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The SIP servlet standard offers a familiar Java application programming interface (API) for developing Session Initiation Protocol (SIP) applications, and the upcoming version 1.1 specification standardizes how multiple SIP servlet applications are composed and invoked to service a communication episode. Such disciplined composition promotes software modularity and reuse, and also helps manage feature interactions. At the core of the application composition framework in the SIP servlet API 1.1 is the Application Router that performs the task of selecting an application to service a SIP request. In this paper, the authors describe an application router implementation based on the Distributed Feature Composition (DFC) architecture routing algorithm (DFC-AR). While the DFC-AR is designed to be simple so it can serve as a sample implementation, it is also sufficiently powerful for real-world VoIP service deployments. The DFC-AR has been proposed to be the default AR in the reference implementation of the 1.1 specification.

We describe some of the challenges and problems as we move from the world of plain old telephony services (POTS) to the promise of Internet-based pretty amazing new services (PANS). We present a set of ideas that relate the architectural evolution of networks and services to the underlying changes in technology. After examining the motivations behind the drive to Internet multimedia communications, we discuss the distribution of service intelligence in the future communications architecture. As with any period of evolution, thorny problems arise regarding interworking between the two network architectures. A brief exploration of the Intelligent Network (IN) is presented as a solution to address interworking. Finally, we examine how the transition to an Internet-based system might affect how transport and services are billed for.