Cooperating with free riders in unstructured P2P networks

Free riding is a common phenomenon in peer-to-peer (P2P) file sharing networks. Although several mechanisms have been proposed to handle free riding—mostly to exclude free riders, few of them have been adopted in a practical system. This may be attributed to the fact that the mechanisms are often nontrivial, and that completely eliminating free riders could jeopardize the sheer power of the network arising from the huge volume of its participants. Rather than excluding free riders, we incorporate and utilize them to provide global index service to the files shared in the network, as well as to relay messages in the search process. The simulation results indicate that our mechanism not only can shift the query processing load from non-free riders to free riders, but can also significantly boost the search efficiency of a plain Gnutella. Moreover, the mechanism is quite resilient to high free riding ratio.