Scalability and Peer Churning in IP-TV: an Analytical Insight

Peer-to-peer (P2P) technology for TV broadcasting over the Internet is becoming more and more popular in the very last years. This paper introduces a network-wide metric to assess the efficiency of P2P streaming systems and develops a mathematical model to explain: (i) the scalability of such architectures with the number of peers, as evidenced by recent measurements; (ii) the initial decrement of efficiency (hence, quality) when a sharp increase in the number of peers in system occurs, as reported by experimental data. As for the second point, the proposed model builds upon the fundamental remark that when a peer first joins the system, it has no video content to share with others: its upload contribution is null for an initial time interval and the new peer behaves as a free rider. Three situations concerning the system reaction to the requests of the new entering peers are examined: full compensation; partial compensation; no reaction at all. Depending on the system answer and on its extent, system efficiency is shown to exhibit different time trends.