Applicability and Limitations of Locality-Awareness in BitTorrent File-Sharing

The BitTorrent file-sharing application has recently been criticized for its undesirable impact on the underlying native network[9, 11]. This is primarily attributed to the selfish peer selection decision of individual peers, which is often unconcerned about network-level repercussions. To reduce the impact, many researchers[9, 13], as well as vendors[2, 15], have proposed the idea of biasing peer selection to favor local peers, thereby using locality-awareness to reduce inter- AS traffic. However, we find that the effectiveness of locality has a narrow scope and is not as effective in all scenarios. Using a discrete-event simulation of the BitTorrent swarm, we show that locality is of use only in provider networks with a large number of peers, and only when the individual peers have a healthy number of neighbors that are external to the local AS. We address these shortcomings of achieving locality by presenting the preliminary design of a price-based neighbor selection scheme, which helps ISPs reduce the cost incurred in a controller manner.