Locality Analysis of BitTorrent-Like Peer-to-Peer Systems

Abstract

Peer-to-peer (P2P) traffic is arguably the biggest contributor to today's Internet traffic. So far, very limited effort has been paid to theoretically analyze the effect of bringing locality-awareness into P2P applications. In this paper, we analyze three locality-awareness policies for BitTorrent-like system: tracker locality(neighbor selection), choker locality(choking and unchoking) and picker locality(piece picking). Based on an H-sphere model which captures the essential property of Internet topology, we analyze how much network load saving can be expected for these locality policies, as well as their impact to the downloading efficiency of the system. Through analytical study and simulation, we have the following findings. First, when the system enters the steady state, the locality policies proposed in this paper can achieve the same downloading efficiency as the standard BitTorrent system. Second, these locality policies can significantly alleviate the traffic load on the Internet. Finally, we find that there exists no all-around winner. Instead, each policy performs the best under different system configuration parameters, such as number of unchoked peers.