Early delivery totally ordered multicast in asynchronous environments

The authors present the construction of a multicast service, called agreed multicast, that guarantees that messages arrive reliably and in the same total-order to all their destinations. ToTo, a novel protocol, implements the agreed multicast service of Transis, a communication subsystem for the High Availability project, currently developed at the Hebrew University of Jerusalem. This service is desired in distributed systems, and supports high level coordination among groups of processes in distributed applications. The ToTo protocol is genuinely symmetric and fairly simple for implementing. It provides early delivery latency, and requires as little as n/2 messages for forming agreement on the order of delivery. Experimental results show up to O(log (n)) speedup over previous protocols, which matches the authors´ prediction of the expected speedup. Using the Transis membership service, ToTo can operate in a dynamic environment, and continue to form an agreed total order among the connected machines despite failures and recoveries.