Abstract
François Massoulié, from Thomson, presented the peer-to-peer transmission of information, which is dominant for the (legal or illegal) distribution of films or music on the Internet, and now occupies 80% of Web bandwidth. The idea is not to use a centralized server, but to transform each receiver of a stream into a transmission relay for that stream. Viruses were the first application of this technique; their name shows that they spread epidemically. F. Massoulié detailed the central problem of choosing the packets of information to be relayed at each instant by a terminal. Subtle variations in algorithms can produce very different results. The best algorithm seems to be to send the last useful packet from the transmitter to a random target, which is far from intuitive. This broadcast provides a throughput arbitrarily close to optimal, with optimal delay.
Peer-to-peer is very simple and very efficient, albeit based on random and decentralized decisions. Research is now focusing on other applications, such as large-scale distributed computing on a large number of remote processors.
