On the Role of Helpers in Peer-to-Peer File Download Systems: Design, Analysis and Simulation

While BitTorrent has been successfully used in peerto-peer content distribution, its performance is limited by the fact that typical internet users have much lower upload bandwidths than download bandwidths. This asymmetry in bandwidth results in the overall average download speed of a BitTorrent-like file download system to be bottle-necked by the much lower upload capacity. This motivates our approach in which we utilize idle users’ spare upload capacity to significantly improve the download speed beyond what can be achieved in a conventional BitTorrent network. We show that this is possible even if these idle users (or helpers) download only a tiny fraction of the file. In fact, in terms of uplink utilization, these helpers can be almost as effective as seeders for medium to large swarms. In this work, we design such a system that is fully compatible with the existing clients who conform to the BitTorrent protocol, analyze its steady-state performance and present simulation results.