Developing applications over a distributed and asynchronous architecture without the need for synchronization services is going to become a central track for distributed computing. This research track will be central for the domain of autonomic computing and self-management. Distributed constraint solving, distributed observation, and distributed optimization, are instances of such applications. This paper is about distributed observation: we investigate the problem of distributed monitoring of concurrent and asynchronous systems, with application to distributed fault management in telecommunications networks. Our approach combines two techniques: compositional unfoldings to handle concurrency properly, and a variant of graphical algorithms and belief propagation, originating from statistics and information theory.