Powering down for energy efficient peer-to-peer file distribution

Peer to peer (P2P) techniques can reduce the time for file distribution, yet require peers to stay ON to assist others download. We study the total time that peers need to be ON to distribute a file from a server to a set of peers. We show that a P2P system optimized for energy efficiency can consume half the energy of one optimized to minimize down-load time, with minimal additional delay. To achieve this, peers finish in increasing order of upload capacity, and turn off as soon as they finish downloading. We show that the optimal solution is complex, even for as few as three peers, and advocate heuristics for large networks.