The Seeder Promotion Problem: Measurements, Analysis and Solution Space

BitTorrent has become the de-facto standard for peer-to-peer content delivery, however, it has been found that it suffers from one fundamental problem: the long-term availability of content. Previous work has attributed this to what is termed the seeder promotion problem in which peers refuse to continue serving content after their own download has completed. As of yet, no deployed solution exists to this problem. In this paper, we objectively investigate the solution space for dealing with the seeder promotion problem. Specifically, both single-torrent and cross-torrent approaches are investigated to ascertain which is superior based on three key metrics: availability, performance, and fairness. To achieve this, two large-scale BitTorrent measurement studies have been performed which include 46K torrents and 29M users. Through these, we first quantify the seriousness of the seeder promotion problem before exploiting the data logs to execute accurate trace-based simulations for the different solutions considered. Using the results, we ascertain and describe the different trade-offs between the four general solutions: extending seeding times, cross-torrent bartering, local persistent histories, and global shared histories. We find that single-torrent solutions are profoundly impractical when considering the user behaviour observed in our studies. In contrast, we discover that the different cross-torrent approaches can offer a far more effective solution for satisfying (to varying degrees) the need for high availability, good performance, and fairness between users.