P2P as a CDN: A new service model for file sharing

Traditional content distribution networks (CDNs), such as Akamai, replicate content at thousands of servers worldwide in an attempt to bring it closer to end users. Recent years have, however, brought a surge of peer-to-peer (p2p) systems that have demonstrated the ability both to help traditional CDN operations and to effectively disseminate content as independent applications. Unfortunately, this p2p surge has created significant problems to network operators by generating large volumes of inter-AS traffic. In this paper, we demonstrate that stepping back and applying traditional CDN design principles to p2p systems can help solve these emerging problems. In particular, focusing on the BitTorrent swarming protocol, we show that our new service model can, in the common case, reduce inter-AS traffic by 45-75%. Moreover, in scenarios when ISPs are shaping inter-AS traffic, it speeds up download times by 60% for the most popular torrents. Our approach bases on disproving the common wisdom that the current peer altruism in p2p systems (BitTorrent in particular) is insufficient. We thus abandon the common approach of deploying novel incentives for cooperation, and focus on designing methods to effectively utilize existing system resources. We show that controlled regional-based content replication, common for the traditional CDN design, can effectively achieve this goal. We implement our system and demonstrate that it effectively scales. Moreover, it is incrementally deployable and brings significant benefits in partial deployment scenarios. ISPs and network regions in which the system gets deployed can resolve their inter-AS traffic problems instantly and autonomously, i.e., without any inter-ISP collaboration and without requiring that the system gets deployed in the entire Internet.