An Optimal Causal Broadcast Protocol in Mobile Dynamic Groups

In Group Communication Systems (GCS), causal message ordering is an essential tool to ensure interaction among group members in a consistent way. In several group-based applications, the exchanged information is often diffused to all members. Using a multicast protocol to ensure this broadcast should make the definition of data structures not optimal for this kind of applications. In this paper, we propose a simple and optimal causal broadcast protocol which copes with the dynamically changing groups in mobile environments. The protocol depends on two simple, yet powerful ideas. The first depends on the use of the immediate dependency relationship in the construction of control information, resulting in O(1) message overhead. When the second original idea depends on considering the join and leave requests as data messages. This ensures a consistent perception of the communication done in the group and makes no need to a coordination phase in the installation of a new view.