A Complementary Modularization for Communication Protocols

Current techniques for protocol design focus on modules that encapsulate the protocol engines that execute on different network nodes. While this modularization is invaluable for independent implementation of network elements, we believe it does not adequately support the design, analysis, or evolution of a protocol. In this paper, we propose a complementary modularization that tackles this problem and is driven rather by the “cross-cutting” aspects of protocol engines. In particular, we report on our experiences with the Session Initiation Protocol (SIP), which is the signaling protocol in the IETF suite of IP telephony standards. SIP has attracted great attention in the telecommunications industry, and there are already many commercial products based on SIP. Since the protocol has already reached a high degree of complexity and will continue to evolve, it is an ideal candidate for our studies.