SWIFT: A System With Incentives For Trading

In this paper, we present the design of a credit-based trading mechanism for peer-to-peer file sharing networks. We divide files into verifiable pieces; every peer interested in a file requests these pieces individually from the peers it is connected to. Our goal is to build a mechanism that supports fair large scale distribution in which downloads are fast, with low startup latency. We build a trading model in which peers use a pairwise currency to reconcile trading differences with each other and examine various trading strategies that peers can adopt. We show through analysis and simulation that peers who contribute to the network and take risks receive the most benefit in return. Our simulations demonstrate that peers who set high upload rates receive high download rates in return, but free-riders download very slowly compared to peers who upload. Finally, we propose a default trading strategy that is good for both the network as a whole and the peer employing it: deviating from that strategy yields little or no advantage for the peer.