Experimentation of Group Communication Protocols

Abstract

In peer-to-peer (P2P) overlay networks, a group of n (= 2) peer processes have to cooperate with each other. Each peer directly 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 like linear clock (LC) and vector clock (VC) are used to causally order messages. Some pair of messages not to be causally ordered are unnecessarily ordered since message length is O(1) in the LC protocol. On the other hand, no message is unnecessarily ordered in the VC protocol. 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 precise physical clock which is synchronized with a time server in NTP. In this paper, we discuss how to causally deliver messages in a scalable group with hybrid clock (HC) which takes advantage of LC and PC in order to reduce the number of messages unnecessarily ordered. The HC protocol is implemented and some experimentations are presented in this paper. We show unnecessarily ordered messages can be reduced in the HC protocol compared with the LC protocol through the experimentations.