A Scalable Group Communication Protocol on P2P Overlay Networks

In peer-to-peer (P2P) overlay networks, a group of n (≥2) peer processes have to cooperate with each other. P2P systems are in nature scalable and distributed, Each peer sends messages to every peer and receives messages from every peer in a group. In group communications, each message sent by a peer is required to be causally delivered to every peer. Types of logical clocks are used to causally order messages, linear and vector clocks. The linear clock can be used in a scalable group since message length is O(1). However, some pair of messages not to be causally ordered are unnecessarily ordered. On the other hand, no messages are unnecessarily ordered in the vector clock. However, the vector clock cannot be adopted in a scalable group due to the message length O(n). Recently, processes on each computer can read more process is obtain more process more time by reading a physical clock is synchronized with time servers. In this paper, we discuss how to causally deliver messages in a scalable group by taking advantage of linear and physical clocks. Here, the number of pairs of messages unnecessarily ordered in the linear clock can be also reduced.