Abstract. We examine extensions to the pi-calculus for representing basic elements of distributed systems. In spite of its expressiveness for encoding various programming constructs, some of the phenomena inherent in distributed systems are hard to model in the pi-calculus. We consider message loss, sites, timers, site failure and persistence as extensions to the calculus and examine their descriptive power, taking the Two Phase Commit Protocol (2PCP), a basic instance of an atomic commitment protocol, as a testbed. Our extensions enable us to represent the 2PCP under various failure assumptions, as well as to reason about the essential properties of the protocol.