Decentralized consensus protocols

Abstract

The goal of decentralized consensus protocols is to exchange information among computers so that each computer acquires information held by every other computer in the system. The authors introduce a unifying framework which generalizes these decentralized consensus protocols. A necessary and sufficient property for consensus protocols, which uses k round of message exchange, is presented. S. Yuan and A.K. Agrawala's (1988) k-dimensional array based protocol can be viewed in this unifying framework. The authors introduce a novel class of protocols within the unifying framework, called quorum-based protocols. Quorum-based protocols are obtained by observing only the necessary properties which must be maintained. They use two rounds of message exchange (i.e. k=2) and have the property that the first and second rounds of message exchange use the same connection. This property may be exploited if the underlying network provides connection-oriented service. Quorum-based protocols include the centralized protocol and T.V. Lakshman and A.K. Agrawala's (1986) protocol. By applying finite projective planes directly, the authors obtain a protocol which reduces the number of required messages to half the number required in Lakshman and Agrawala's protocol. >