A Novel Optimistic Unchoking Algorithm for BitTorrent

Optimistic unchoking plays an important role in BitTorrent peer-to-peer (P2P) file sharing networks. Peers use optimistic unchoking to find upload bandwidth information about their neighbors. However, free-riders can also take advantage of optimistic unchoking and download from the network without uploading anything. In this paper, we propose a novel optimistic unchoking algorithm for BitTorrent. The main purposes of our algorithm are to prevent free-riding and to improve the efficiency of optimistic unchoking. We then propose a stochastic model to analyze the performance of our algorithm. We also verify the results by simulations. Both theoretical and simulation results show that our algorithm can effectively prevent free-riding and significantly improve the download rate of normal peers at the same time.