TOTALLYORDERED BROADCAST IN THE FACE OF NETWORK PARTITIONS Exploiting Group Communication for Replication in Partitionable Networks

We present an algorithm for Totally Ordered Broadcast in the face of net work partitions and process failures using an underlying group communi cation service as a building block The algorithm always allows a majority or quorum of connected processes in the network to make progress i e to order messages if they remain connected for su ciently long regard less of past failures Furthermore the algorithm always allows processes to initiate messages even when they are not members of a majority compo nent in the network These messages are disseminated to other processes using a gossip mechanism Thus messages can eventually become totally ordered even if their initiator is never a member of a majority component The algorithm guarantees that when a majority is connected each mes sage is ordered within at most two communication rounds if no failures occur during these rounds