Decidable topologies for communicating automata with FIFO and bag channels

Abstract

We study the reachability problem for networks of finite-state automata communicating over unbounded perfect channels. We consider communication topologies comprising both ordinary FIFO channels and bag channels, i.e., channels where messages can be freely reordered. It is well-known that when only FIFO channels are considered, the reachability problem is decidable if, and only if, there is no undirected cycle in the topology. On the other side, when only bag channels are allowed, the reachability problem is decidable for any topology by a simple reduction to Petri nets. In this paper, we study the more complex case where the topology contains both FIFO and bag channels, and we provide a complete characterisation of the decidable topologies in this generalised setting. © 2014 Springer-Verlag.