Resource demand and supply in BitTorrent content-sharing communities

BitTorrent is a widely popular peer-to-peer content distribution protocol. Unveiling patterns of resource demand and supply in its usage is paramount to inform operators and designers of BitTorrent and of future content distribution systems. This study examines three BitTorrent content-sharing communities regarding resource demand and supply. The resulting characterization is significantly broader and deeper than previous BitTorrent investigations: it compares multiple BitTorrent communities and investigates aspects that have not been characterized before, such as aggregate user behavior and resource contention. The main findings are three-fold: (i) resource demand - a more accurate model for the peer arrival rate over time is introduced, contributing to workload synthesis and analysis; additionally, torrent popularity distributions are found to be non-heavy-tailed, what has implications on the design of BitTorrent caching mechanisms: (ii) resource supply - a small set of users contributes most of the resources in the communities, but the set of heavy contributors changes over time and is typically not responsible for most resources used in the distribution of an individual file; these results imply some level of robustness can be expected in BitTorrent communities and directs resource allocation efforts; (iii) relation between resource demand and supply users that provide more resources are also those that demand more from it; also, the distribution of a file usually experiences resource contention, although the communities achieve high rates of served requests. (C) 2008 Elsevier B.V. All rights reserved.