Peer Selection Strategies for Improved QoS in Heterogeneous BitTorrent-Like VoD Systems

The efficiency of Bit Torrent in disseminating content has inspired a number of P2P protocols for on-demand video streaming (VoD). Prior work on adapting Bit Torrent to VoD mainly focused on the piece selection policy, since streaming requires a somewhat "in order" download progress. Conversely, not much effort has been spent into adapting Bit Torrent\´s peer selection policy, where nodes mainly serve those that have recently uploaded to them at the highest rates. This mechanism incentivizes cooperation among peers but, in a heterogeneous system (i.e. where peers have different bandwidth capacities), it causes faster peers to receive higher download speeds than slower peers. This might hurt the system\´s ability of providing as many nodes as possible with the minimum download speed necessary to sustain the video playback rate. Furthermore, peers gain little utility in downloading at rates much higher than the video playback rate. Inspired by these observations, in this work, we extend the peer selection mechanism of an existing Bit Torrent-like VoD protocol, give-to-get (G2G), with techniques that allow peers to relax their reciprocity-based peer selection and choose more random nodes when their current QoS is high. In this way, more peers can be granted a good QoS and free-riding is tolerated only when bandwidth resources are abundant. To demonstrate the benefits of our approach, we present extensive simulations of the introduced techniques.