Designing a Tit-for-Tat Based Peer-to-Peer Video-on-Demand System

Video-on-demand (VoD) is a next-generation Internet application of increasing interest allowing users to start watching a movie almost instantaneously by downloading the video on-the-fly. Provided that all users contribute to the system, shifting to the P2P paradigm allows efficient broadcast with a limited-bandwidth source. Until now, most P2P VoD systems rely on the willingness of peers to collaborate and only few use incentive mechanisms. In VoD applications pieces are downloaded in order. This prevents to directly apply a BitTorrent-like tit-for-tat incentive scheme. Although existing solutions based on random exchanges have good performance, we advocate the use of structure in P2P VoD applications to achieve high playback rates. In this paper we propose a decentralized piece dissemination scheme built using loosely coupled structures. Peers are grouped into clusters depending on their playback position. Swarming is performed inside the clusters while distributed feeding ensures that less advanced clusters get missing pieces from more advanced ones. Our simulations demonstrate that structured dissemination improves from 61% with the competitor to 77% of the achievable playback rate