Fewest Common Hops (FCH): An Improved Peer Selection Approach for P2P Applications

Underlay-unawareness in P2P systems can result in sub-optimal peer selection for overlay routing and hence poor performance. The majority of underlay aware proposals for peer selection focus on finding the shortest overlay routes by selecting the nearest peers according to proximity. However, in case of multiple and parallel downloads, if the underlay paths between a downloader and its selected nearest peers share a bottleneck, this can cause congestion, leading to performance deterioration instead of improvement. This effect was neglected in previous work because, in today´s Internet, the bottleneck is usually not shared as it is the end user´s access link. This is no longer the case in more modern scenarios, e.g. with FTTH or with upcoming in-network caching techniques such as DECADE. We propose an improved peer selection approach for P2P applications called Fewest Common Hops (FCH) that ensures proximity based node selection having maximum path disjointness. It is a client based, infrastructure independent heuristic to optimize download time for multiple and parallel downloads in P2P content distribution applications. Simulations show that, even when FCH is implemented in the simplest possible fashion (using only traceroute), it can significantly decrease the download time.