A Simple Ordered and Reliable Group Multicast Protocol

In this paper, we propose a simple and efficient token-based protocol that minimizes the {\em delivery-time} while maintaining an acceptable level of reliability. It guarantees a total order for all delivered messages within a group. The novel feature of the protocol is the ability to choose the sites within a group from which acknowledgements are to be received prior to delivery of a message. This choice can be made on a per message basis. The paper also discusses the trade-offs involved in choosing a large set of acknowledgers versus a small set. We analyze the effects of the size of this set on delivery time, availability, and robustness of the system. We also state and prove the properties guaranteed by the protocol.