Hierarchical protocol for broadcast-type group communication

Large numbers of peer processes are cooperating by exchanging messages in automatic, peer-to-peer systems. In this paper, we discuss a hierarchical group protocol aiming at reducing communication and computation overheads for a group of large number of processes. A hierarchical group is hierarchically composed of subgroups. Each subgroup supports its own mechanism to causally order messages. Even if messages are causally ordered in one subgroup, the messages may not be causally ordered in another subgroup. We discuss how to globally causally order messages in subgroups. In addition, we evaluate the protocol.