Performance investigation on request collisions in peer-to-peer live streaming systems: Problems and algorithms

A fundamental design issue in a peer-to-peer (P2P) live streaming system is how peers select neighbors for downloading media pieces. Inappropriate selection of neighbor peers for piece downloading can exacerbate the collisions of requests among peers and therefore degrade the system performance. In this paper, we first show how severe the request collision problem could be and also to which degree it could affect the performance of a P2P live streaming system by extensive measurements and simulations. We then propose a novel neighbor peer selection algorithm for piece downloading. In the algorithm, each peer needs to infer the severity of request collisions at each of its neighbors based on the most recent request-with-no-response history. Based on this information, each peer always sends requests to those neighbors with low collision probability at high priority. This algorithm can effectively avoid the difficulty in obtaining accurate network conditions and/or peer availability and also greatly reduce the signaling overhead for exchanging residual-capacity-related information among peers. In addition, the algorithm is easy to implement. Simulation results show that the proposed algorithm can effectively alleviate the request collision problem and improve the system performance.