On the Efficiency and Cost of Introducing QoS in BitTorrent

BitTorrent is currently a de facto standard for scalable content-distribution. However, its peer-to-peer model for resource allocation does not provide high availability and its performance depends on best-effort contributions given by peers. This has motivated several content-providers to use a hybrid model in which they operate a superpeer in order to attain a higher quality of service. In this paper, we use BitTorrent traces and analytical modelling to investigate the cost incurred by such an entity in relation to the benefits it can provide to the system.