Electing a Leader in a Synchronous Ring

Abstract

We consider the problem of electing a leader in a synchronous ring of n processors. We obtain both positive and negative results. One the one hand, we show that if processor ID's are chosen from some countable set, then there is an alorithm which uses only O(n) messages in the worst case. On the other hand, we obtain two lower bound results. If the algorithm is restructed to use only comparisons of ID's, then we obtain an Ω(n log n) lower bound for the number of messages required in the worst case. Alternatively, there is a (very fast-growing) function f with the following property. If the number of rounds is required to be bounded by some t in the worst case, and ID's are chosen from any set having at leas f(n,t) elements, then any algorithm requires Ω(n log n) messages in the worst case.