Design choices for weak-consistency group communication

Many wide-area distributed applications can be implemented using distributed group communication, a mechanism for coordinating the activities of related processes running at different sites. We have developed a modular architecture for group communication systems that can be used to build a system tailored to application requirements. We focus on weak consistency mechanisms for group communication, since these allow highly efficient operation on wide-area internetworks. We examine several design choices that can be made in building a weakly-consistent group communication mechanism, and discuss the decisions we made in building two very different wide-area applications. The architecture accommodates both systems well, and allows several application-specific decisions that increase efficiency and flexibility.