SIP-Based Technology for Compositional Services

Our succeessful experiences with Distributed Feature Composition have shown the value of building IP-based multimedia services compositionally.

SIP is now the dominant signaling protocol for building multimedia services on top of the Internet Protocol (IP). Because little is known about building SIP services compositionally, a team of AT&T researchers is working to adapt what we have learned from DFC, and make it available to the SIP community. The team consists of:

• Greg Bond
• Eric Cheung
• Tom Smith
• Pamela Zave

We have converted our DFC implementation to a version that runs inside vendor-supplied SIP Servlet containers. Two of the crucial components of this work are our ECharts programming language and our ECharts for SIP Servlets (E4SS) development kit, both available as open-source software.

Another crucial component of this work is the new Java Community Process standard for SIP Servlet containers, which was designed to support the DFC routing algorithm as the mechanism for composing SIP servlets. A DFC router is available with E4SS.

A fourth crucial component of this work is StratoSIP, which is a high-level language for programming SIP Servlets with the benefit of DFC abstractions.

Finally, we are now investigating converged services, which combine telecommunications with Web services. We have some prototype tools already, and expect to make significant additional progress.

Understanding SIP through Model-Checking

"Understanding SIP through model-checking" reports on a project to build Promela models of SIP, and to verify them with the Spin model checker (Pamela Zave; Proceedings of the Second International Conference on Principles, Systems and Applications of IP Telecommunications, pages 256-279, Springer-Verlag LNCS 5310, 2008). The following models and analysis results are an updated and corrected version of the models and results presented in the paper:

• basicraw.pml is a basic model of invite dialogs in SIP, with some restrictions in scope.
• transraw.pml is a model of invite dialogs in SIP, assuming exactly one TCP connection for transactions initiated by the UAC, and exactly one for transactions initiated by the UAS.
• fiforaw.pml is like the basic model, except that signaling is constrained to be FIFO (in other words, there is exactly one TCP connection per invite dialog).
• basicread.pml, transread.pml, and fiforead.pml are more readable versions of their respective raw models. Unreachable code and assertions used only to check reachability have been removed.
• basiccheck.txt, transcheck.txt, and fifocheck.txt are analytic results for their respective models. They contain the output of the Spin model checker.
• summary.txt summarizes the analytic results in a table, so that the models can be compared.
• notes.txt contains notes referred to in the models.