Priority-Based Scheme for File Distribution in Peer-to-Peer Networks

Peer-to-Peer (P2P) networks are distributed systems where no central authority rules the behavior of the individual peers. A typical application is the sharing of files of some class (movies, music, ...), our object of interest here. These systems relay on the voluntary participation of the peers to help each other. However, it is not uncommon to find users that have initiated a file transfer and decide to leave the system before the end of the download. This is a particularly harmful behavior due to the resources, such as bandwidth or energy, wasted in such an aborted process. This negative effect is amplified when the system's conditions are such that the peers are not downloading at the maximum capacity, i.e., the downloading bandwidth is underutilized. This is because in these conditions, there are not enough peers uploading the file, and a part of the bandwidth is wasted on peers that do not share their resources to the network once they leave the system. In this paper, a priority scheme is presented for a BitTorrent-based P2P network where the peers that are more likely to remain longer in the system are served first, over peers that are statistically more likely to abort the download. By giving priority to peers that are likely to go through the complete file download, the successful download rate for the peers that remain longer in the system is increased and the resources of the system are better utilized. The proposed scheme is analyzed by means of different models, in order to find the steady-state performance of the network.