Self-stabilizing robots in highly dynamic environments

This paper deals with the classical problem of exploring a ring by a cohort of synchronous robots. We focus on the perpetual version of this problem in which it is required that each node of the ring is visited by a robot infinitely often. The challenge in this paper is twofold. First, we assume that the robots evolve in a highly dynamic ring, i.e., edges may appear and disappear unpredictably without any recurrence, periodicity, or stability assumption. The only assumption we made (known as the temporal connectivity assumption) is that each node is infinitely often reachable from any other node. Second, we aim at providing a self-stabilizing algorithm to the robots, i.e., the algorithm must guarantee an eventual correct behavior regardless of the initial state and positions of the robots. In this harsh environment, our contribution is to fully characterize, for each size of the ring, the necessary and sufficient number of robots to solve deterministically the problem.