NAP: practical fault-tolerance for itinerant computations

One use of mobile agents is support for itinerant computation (D. Chess et al., 1995). An itinerant computation is a program that moves from host to host in a network. Which hosts the program visits is determined by the program. The program can have a pre-defined itinerary or can dynamically compute the next host to visit as it visits each successive host; it can visit the same host repeatedly or it can even create multiple concurrent copies of itself on a single host. Itinerant computations are susceptible to processor failures, communications failures, and crashes due to program bugs. NAP is a protocol for supporting fault tolerance in itinerant computations. It employs a form of failure detection and recovery, and it generalizes the primary backup approach to a new computational model. The guarantees offered by NAP as well as an implementation for NAP in TACOMA are discussed.