BitTorrent has attracted attention from researchers and the press for its wide deployment and explicit goal of eliminating free-riding, but many of the most important peers in BitTorrent operate outside of its incentive mechanisms. Altruistic seeders help bootstrap new peers and provide a significant fraction of the global upload bandwidth. We have taken an empirical approach to understanding seeders by studying 35 BitTorrent sites with nearly four million users at any moment over several weeks. Our study focuses on two aspects of seeders. First, we looked at the relationship between the number of seeders and bandwidth utilization. A case study of a Linux distribution network showed that as bandwidth utilization increased, the rate of seeding decreased. Second, we looked at the relationship between site attributes and the number of seeders. A survey of 34 BitTorrent sites over two weeks found that the presence of niche-content (e.g. only anime, hip-hop, or Linux files), merchandise for sale (e.g. t-shirts with the site URL), and negative reinforcement (e.g. a posted list of the 10 least contributing peers) correlated positively with the rate of seeding.
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