  Solving free riding and selecting a reliable service provider in P2P networks
has been separately investigated in last few years. Using trust has shown to be
one of the best ways of solving these problems. But using this approach to
simultaneously deal with both problems makes it impossible for newcomers to
join the network and the expansion of network is prevented. In this paper we
used the game theory to model the behavior of peers and developed a mechanism
in which free riding and providing bad service are dominated strategies for
peers. At the same time newcomers can participate and are encouraged to be
active in the network. The proposed model has been simulated and the results
showed that the trust value of free riders and bad service providers converge
to a finite value and trust of peers who provide good service is monotonically
increased despite the time they join the network.
