An approach to constructing modular fault-tolerant protocols

Modularization is a well-known technique for simplifying complex software. An approach to modularizing fault-tolerant protocols such as reliable multicast and membership is described. The approach is based on implementing a protocol´s individual properties as separate microprotocols and then combining selected microprotocols using an event-driven software framework. A system is constructed by composing these frameworks with traditional network protocols using standard hierarchical techniques. In addition to simplifying the software, this model helps clarify the dependencies among properties of fault-tolerant protocols and makes it possible to construct systems that are customized to the specifics of the application or underlying architecture. An example involving reliable group multicast is given, together with a description of a prototype implementation using the SR concurrent programming language