Timestamp Acknowledgments for Determining Message Stability

Determination of message stability is important for multicast group communication systems, both for assuring applications that messages have been delivered and also for message buffer management. We present a protocol for determining message stability that uses a single scalar timestamp to acknowledge messages from many sources. The protocol avoids the linear growth in the acknowledgment size that occurs with vector acknowledgment protocols. Compared to other protocols, the protocol consumes significantly less network bandwidth, and its latency to the determination of message stability is only slightly larger. Synchronized physical clocks are shown to yield lower latency than logical clocks. We also present a simple connection establishment and group membership protocol for use in conjunction with the message stability protocol.