A design method for communications software evolution

This paper discusses a verification method for communication services on a network in which new service functions are added to only some of the network nodes. Communication networks are becoming larger, and new functions are constantly required for communication services. In a large-scale network, however it as very difficult to update all node functions simultaneously. In this case, in a single network there will be nodes that have both new and existing functions and other nodes having only existing functions. This situation might result in illegal actions in communications between functionally updated nodes and non-updated nodes. We clarify the fundamental properties of illegal actions, present an algorithm for detecting them and show that the algorithm is practical enough from the viewpoint of the order of complexity