A Protocol for Making an Agreement in a Peer-to-Peer (P2P) Society

There are many discussions on agreement protocols of multiple peer processes where every peer just aims at agreeing on one value out of values shown by the peers. In human societies, agreement procedures are so flexible that persons can change their opinions and can use not only all-condition but also various types of agreement conditions in a meeting. In this paper, we discuss a flexible agreement protocol of multiple peer processes (peers) by taking account the human behaviour in social agreement procedures. Each peer first takes a value v₁ and notifies the other peers of the value v₁. A peer in turn receives values from other peers. Unless a set of the values from all the peers satisfy an agreement condition, the peer p_i can take another value v₂. In order to model the social human behaviour, we already discuss E- and P-precedent relations rarr_i ^E and rarr_i ^P on values of a peer p_i. The relations v₁ rarr_i ^E v₂ and v₁ rarr_i ^P v₂ show that a peer p_i can take a value v₂ after taking v₁ and prefers v₁ to v₂, respectively. If a peer autonomously takes values based on its precedent relations, the processes might not make an agreement even if there exist a satisfiable tuple of values. In order to efficiently make an agreement, peers are required to be coordinated. In this paper, we introduce methods for coordination of multiple peer processes, forward, backward, and null.