Lyapunov stability and performance of user-assisted Video-on-Demand services

Currently, most video on-demand services offered over the Internet do not exploit the idle resources available from end-users, including YouTube. We present a taxonomic analysis of user-assistance in video on-demand systems, where users are both clients and servers, helping with the task of video distribution. From a theoretical perspective, we develop a deterministic fluid model suitable for sequential systems. We mathematically prove the Peer-to-Peer Sequential Fluid Model is globally stable in the Lyapunov sense, no matter the network parameters of the cooperative system. We theoretically prove that cooperative systems always outperform non-cooperative solutions. From a practical point of view, a caching problem is proposed and discussed in order to tackle technological concerns to massively distribute popular videos on-demand. The goal is to distribute video items into repositories minimizing the waiting times of end-users. The caching problem is inside the class of NP-Complete computational problems, and heuristically solved with a GRASP methodology enriched with a path-relinking technique. Predictions inspired in a statistical analysis of real-life YouTube traces suggest the introduction of cooperation is both robust and economically attractive. These results highlight the harmony between our theoretical development and practice. (C) 2015 Elsevier B.V. All rights reserved.