A measurement study on swarm evolution of BitTorrent

Studying the BitTorrent (BT) swarm evolution in different time scale is important to design accurate BT simulators and improve the performance of current BT systems. In this paper, we develop a hybrid measurement system incorporating both active and passive approaches. By exploiting DHT and PEX protocols in addition to traditional resources, we collect more extensive information compared to prior measurement systems. Based on the measurement results, we study the swarm evolution with different population in minute/hour/day scales, and discover that: (1) The swarm peer population is unbalanced, in that 74.6% torrents have no more than 1000 peers, (2) The lifetime of torrents can be divided into a fast growing stage, a dramatically shrinking stage, a sustaining stage and a slowly fading out stage in terms of swarm population, (3) Users´ interest and diurnal periodicity are the main factors that influence the swarm evolution. The former dominates the first two stages, while the latter is decisive in the third stage. In this spirit, we raise an improved peer arrival rate model to describe the variation of the swarm population. Comparison results show that our model outperforms the state-of-the-art approach according to root mean square error and correlation coefficient.