A Client-Server Approach to Virtually Synchronous Group Multicast: Speci£cations and Algorithms

This paper presents a formal design for a novel group multicast service that provides virtually synchronous semantics in asynchronous fault-prone environments. The design employs a client-server architecture in which group membership is maintained not by every process but only by dedicated membership servers, while virtually synchronous group multicast is implemented by service end-points running at the clients. Speci£cally, the paper de£nes service semantics for the client-server interface, that is, for the group membership service. The paper then speci£es virtually synchronous semantics for the new group multicast service, as a collection of commonly used safety and liveness properties. Finally, the paper presents new algorithms that use the de£ned group membership service to implement the speci£ed properties. The algorithm that provides the complete virtually synchronous semantics executes in a single message round in parallel with the membership service’s agreement on views, and is therefore more ef£cient than previously suggested algorithms providing such semantics.