Technischer Bericht Modeling Soft State Protocols with SDL

Soft state enables new services to packet-switching networks by introducing a type of state in the network nodes which is refreshed by periodical messages otherwise expire. System designers build protocols that implement soft state concepts based on intuition or on high-level explanations believe that the design is “better” than hard state and soft state implementations should be robust, reliable and interoperable. As states in the network nodes are critical for both applications the and network infrastructure, the operations of soft state protocols, which tend to be designed more and more complex, need to be error-free and deadlock-free. Thus, verification, formal analysis and validation of these protocols become a vital task. In this paper we utilize formal techniques, specifically, Specification and Description Language (SDL) and Message Sequence Chart (MSC), for modeling, analysis and validation of general soft state protocols. We propose a general architecture of state management systems and find several points through the SDL/MSC modeling which may enrich the design, modeling and evaluation of real soft state protocols: 1) modeling these protocols using these techniques is feasible, 2) it can be possible to use these techniques to identify possible design errors and deadlocks/livelocks, which may be caused by imprecise informal specifications of these protocols.