Peer-assisted content distribution in Akamai netsession.

ABSTRACTContent distribution systems have traditionally adopted one of two architectures: infrastructure-based content delivery networks (CDNs), in which clients download content from dedicated, centrally managed servers, and peer-to-peer CDNs, in which clients download content from each other. The advantages and disadvantages of each architecture have been studied in great detail. Recently, hybrid, or 'peer-assisted', CDNs have emerged, which combine elements from both architectures. The properties of such systems, however, are not as well understood. In this paper, we discuss the potential risks and benefits of peer-assisted CDNs, and we study one specific instance, Akamai's NetSession system, to examine the impact of these risks and benefits in practice. NetSession is a mature system that has been operating commercially since 2010 and currently has more than 25 million users in 239 countries and territories. Our results show that NetSession can deliver several of the key benefits of both infrastructure-based and peer-to-peer CDNs - for instance, it can offload 70-80% of the traffic to peers without a corresponding loss of performance or reliability - and that the risks can be managed well. This suggests that hybrid designs may be an attractive option for future CDNs.