The Impact of Policy and Mechanism in the Implementation of Group Communication in a Distributed System

Group communications are becoming increasing important in the development of distributed applications and services. Group communication protocols in both distributed multimedia applications and distributed operating systems offer the programmer a rich paradigm for the easy construction of distributed application. The group communication protocol implementation must provide the basic mechanisms and semantics to allow the application programmer to implement the appropriate policy for a given application. This report examines the implementation aspects of group communication protocols. To provide efficient group communication protocol this report addresses the semantics provided by Message Reliability, Groups Structure, Group Membership, Delivery Semantics, Response Semantics, and Message Ordering of the protocol. In providing these policies the application programmer must be aware of possible limitations of group communication in providing efficient communications. Similarly, the application layer programmer must know the semantics offered by the group communication protocol. In this report we propose a group communication model that provides fast, flexible, and efficient group communications by clearly separating the policy and mechanism of the group communication protocol. RHODOS November 28, 1997