Symmetric and Synchronous Communication in Peer-to-Peer Networks

TL;DR

This paper investigates how symmetric and synchronous communication protocols in peer-to-peer networks can achieve common knowledge among processes, highlighting the importance of CSP's communication primitives for distributed algorithms.

Contribution

It formalizes symmetric peer-to-peer networks and proves CSP with input/output guards enables common knowledge, unlike the restricted version without output guards.

Findings

CSP with input/output guards allows common knowledge in symmetric networks.

Restricted CSP without output guards cannot achieve common knowledge.

Symmetric peer-to-peer networks are formally modeled and analyzed.

Abstract

Motivated by distributed implementations of game-theoretical algorithms, we study symmetric process systems and the problem of attaining common knowledge between processes. We formalize our setting by defining a notion of peer-to-peer networks(*) and appropriate symmetry concepts in the context of Communicating Sequential Processes (CSP), due to the common knowledge creating effects of its synchronous communication primitives. We then prove that CSP with input and output guards makes common knowledge in symmetric peer-to-peer networks possible, but not the restricted version which disallows output statements in guards and is commonly implemented. (*) Please note that we are not dealing with fashionable incarnations such as file-sharing networks, but merely use this name for a mathematical notion of a network consisting of directly connected peers "treated on an equal footing", i.e. not having a client-server structure or otherwise pre-determined roles.)