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Herman's Algorithm: A Brief Survey and Some Recent Results

Talk by Joël Ouaknine (University of Oxford)
Slides

Abstract

Herman's algorithm is a well-studied, two-decades-old synchronous randomised protocol for achieving distributed self-stabilization (or leader election) in a token ring consisting of N processes. The interaction of tokens however makes the dynamics of the protocol fairly difficult to analyse. In particular, the exact worst-case expected stabilisation time of this protocol remains an open problem dating back to the inception of the algorithm, despite a series of partial results, advances and conjectures over the last twenty years.

I will present Herman's algorithm, review some of the existing body of work on it, and present some recent results which improve on the best-known upper bounds for expected stabilisation time. I will also briefly discuss some connections to other scientific areas such statistical mechanics, epidemiology, and Brownian motion.

This is joint work with Stefan Kiefer, Andrzej Murawski, James Worrell, and Lijun Zhang.