Formalizing REST APIs for web-based communication and SIP interworking

Significant research efforts for the convergence of Web and Telecommunication services have been recently spent by research and industry stakeholders. The IETF and W3C are cooperating in specifying how web browsers should evolve to natively support communication services. In this perspective, devising novel mechanisms for the signaling message exchange and possible interworking between Web- and SIP- based systems is a hot topic of research. Indeed, discussions are still ongoing on how differences between REpresentational State Transfer (REST) and Session Initiation Protocol (SIP) models should be coped with. This issue is made more difficult by the lack of rigorous modeling of RESTful systems. In this article we propose a rigorous approach for the design and implementation of REST communication services (e.g., a call service) which leverages formal verification techniques, while while allowing to meet a specific performance requirement (i.e. maximum call setup delay). First, we formalize the call resource behavior through a Finite State Machine representation by modeling and simulating service expected behavior and its interworking with SIP User Agents through a tool for the analysis of communicating state machines. Then, we use the model-checking capabilities offered by the tool for the verification of formal properties. Finally, we implement a prototype that, thanks to the previous formalization step, is shown to be functionally correct, while yielding acceptable performance.