The notion of "superpeer" has been shown to be very effective to increase the scalability of P2P applications. For superpeer systems to work, it is critical to preserve the optimal ratio between the number of superpeers and normal peers participating in the overlay. This requires that peers change dynamically their role (i.e., from superpeer to normal peer and vice versa) in the presence of node arrivals and departures, a problem that is hard to solve if no peer has global knowledge of the network. In this article, we first investigate the feasibility of superpeer ratio maintenance when each peer can decide to be a superpeer independently of each other. We then show how this problem can be treated as an optimization problem, and we propose a distributed algorithm, based on particle swarm optimization (PSO), to solve it. Our simulation results prove the viability of a PSO-based approach for this problem.
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