The BitTorrent Peer Collector Problem

Peer-to-Peer (P2P) systems measurements are still a relevant research topic, since insights in large swarm sizes and churn are not yet available for the BitTorrent network. To improve existing measurement methodology, this work here tackles the aspect of swarm size estimation and complete collection in the BitTorrent network. For this purpose the Coupon Collector Problem is modified and formulated as the BitTorrent Peer Collector (BTPC) Problem. Thus, (a) simulations are used to test simple and maximum likelihood estimation for hidden swarm sizes, (b) an analytical solution to the BTPC problem is presented, and (c) measurements are used to evaluate estimators of the BTPC model. Obtained results show that this estimation works well for classical trackers and that churn constantly influences measurements. Those results show that more peers use the Main-line DHT than a single tracker, however, client implementations challenge those models working well for trackers.