A flexible group communication protocol with hybrid clocks

• Authors: Isamu Tsuneizumi;Ailixier Aikebaier;Tomoya Enokido;Makoto Takizawa
• Venue: Proceedings of the 7th International Conference on Advances in Mobile Computing and Multimedia
• Year: 2009

In distributed applications, a group of multiple peer processes are required to cooperate with each other. Messages sent by peer processes have to be delivered in some order like causal order and total order. In this paper, we discuss a scalable group communication protocol for a group of multiple peers in peer-to-peer (P2P) overlay networks. Due to the message overhead O(n) for the number n of peer processes, the vector clock cannot be used to causally deliver messages. In this paper, we consider a group where every member peer process can use a physical clock which is synchronized with GPS time server in the network time protocol (NTP). The physical clock can be used to temporally order messages while the linear clock can be used to causally order messages. Even if each physical clock is synchronized with a time server, every physical clock does not show the same accurate time. The accuracy of the physical clock depends on distance, i.e. number of routers and traffic in a network. We discuss how the physical and linear types of clocks can be used to temporally and causally order messages in terms of delay time between peer processes and accuracy of each physical clock. In this paper, we discuss a group communication protocol to deliver messages by taking usage of physical clock and linear clock.