Abstract— Group communication services have been successfully used to construct applications with high availability, dependability, and real-time responsiveness requirements. Flowcontrol techniques enable group members to manage their local buffers, which they use to temporarily store multicast updates. Despite buffer overflow being one of the main causes of process failures, flow control has not been studied much in literature. We study different flow-control techniques used in some of the group communication services and present two generic flowcontrol techniques: a conservative and an optimistic technique. All existing flow-control techniques for group communication can be classified as either conservative or optimistic. We then present discrete event simulation results that compare the effect of these two generic flow-control techniques on the performance of two different atomic multicast protocols, a positive acknowledgment protocol and a negative acknowledgment protocol,...