Just found this article which is worth reading especially if you're working in the area of P2P live video streaming.
Tewari, S. and Kleinrock, L., "Analytical Model for BitTorrent- based Live Video Streaming", in Proceedings of IEEE NIME 2007 Workshop, Las Vegas, NV, Jan 2007. PDF
Abstract: Peer-to-peer live video streaming over the Internet has been measured to support over 100,000 concurrent users. While the approach is very attractive, established providers need to understand the performance of such a system before deploying such a system as a frequent loss in quality would jeopardize their reputation. This paper provides an analytical model to inform the design of BitTorrent-based live video streaming solutions. While, given the current broadband deployment scenario, a pure peer-to-peer solution can support only limited streaming rates, our analysis shows that the addition of a well-designed peer-to-peer solution to existing server-based streaming infrastructures can allow substantially higher streaming rates. The efficiency of a BitTorrent-like peer-to-peer solution depends on the peer group size and the number of fragments available for sharing at any given time. Our analysis suggests that the efficiency of the peer-to-peer solution is not sensitive to the size of the peer group for groups larger than 15-20 users. A similar threshold exists for the number of fragments available for sharing at any given time. For live streaming scenarios, this threshold dictates that the fragment size be substantially smaller than the default fragment size in BitTorrent to ensure that the stream latency is small.