Institutionalised Paxos consensus

Abstract

We address the problem of maintaining consistency in systems that are open, decentralised and resource-constrained, where the system components are highly mobile and/or 'volatile'. An example of these systems is found in vehicular ad hoc networks (VANET). Self-organising and norm-governed electronic institutions have been proposed to address these issues, but the problem of maintaining the consistency of conventionally-agreed values (institutional facts) arises due to the fragmentation/aggregation of component clusters, role failure, and revision of agreed values. In this paper, we specify IPCon, an algorithm for Institutionalised Paxos Consensus, which is an extension of the well-known Paxos consensus algorithm for maintaining consistency in static distributed databases. The 'classic' Paxos algorithm is modified to accommodate role-based institutionalised power and extended to allow for dynamic clusters that may change, merge or fragment. We further extend IPCon to allow for the revision of previously agreed parameter values. A proof of correctness for IPCon is given, along with details of an axiomatisation and executable specification of the algorithm in the Event Calculus. These results show that IPCon is a viable method for coordination, consensus formation and collective-choice in self-organising multi-agent systems using electronic institutions.