Stability and Efficiency of Unstructured File Sharing Networks

We propose two unstructured file sharing games, unilateral and bilateral unstructured file sharing games, to study the interaction among self-interested players (users) of unstructured P2P file sharing applications. In a unilateral unstructured file sharing game, players compete for network resources (link bandwidth) by opening multiple connections to each other on multiple paths so as to maximize their individual benefits. A player always allows other players to connect to itself. Multiple concurrent connections are allowed on any path between a pair of players. Per-connection throughput is determined by the transport protocol implemented by users' computers. In a bilateral unstructured file sharing game, users adopt a Tit-for-Tat strategy, under which an active connection between two players is set up only when they both find it beneficial. Two players can set up at most one connection between themselves and bottlenecks occur only at upstream access links in a star network. For both games, we prove the existence of an equilibrium, quantify the efficiency losses of equilibria, and demonstrate the dynamic stability of equilibria in best-response or better-response dynamic game playing processes.