Do BitTorrent-Like VoD Systems Scale under Flash-Crowds?

Abstract

The efficiency of BitTorrent for file sharing has inspired a number of BitTorrent-based P2P protocols for Video-on-Demand (VoD). It has been shown that these systems are scalable in steady-state: the service quality provided to the users does not depend on the number of users in the system. However, it is not well understood how these systems scale under flash-crowds. In this work, we model a general BitTorrent-like VoD system and we find that under a flash-crowd the quality-of-service (QoS) degrades with the number of users. Also, our analysis shows that, at the very beginning of a flash-crowd, the maximum number of simultaneous users that can obtain a given service level is intrinsically related to two fundamental system parameters, namely the initial service capacity and the efficiency of piece exchange of the underlying P2P protocol. Finally, we illustrate the impact of peers turning into seeders (i.e peers that have finished downloading and remain in the system to upload) on the system scale.