Request peer selection for peer-to-peer streaming

Abstract

As the Internet develops and technology evolves, multimedia traffic dominates the Internet. Traditional client-server based video streaming solutions are expensive and suffering from the scalability issue. Inspired by the immense success and efficiency of BitTorrent in distributing file contents to large groups of users, the peer-to-peer (P2P) paradigm has been adopted to provide streaming services including both P2P video-on-demand (VoD) and P2P live streaming.

Among the design challenges, one open yet fundamental question is, how to identify the most suitable neighbor for a peer to make a piece request. We refer this problem as the request peer selection problem. Properly allocating the piece request to potential providers is essential to the system and would help to balance the load at each peer. A well designed request peer selection algorithm increases the requestor’s probability to download the desired piece timely which leads to enhanced video quality and improved playback continuity. This thesis aims to enhance the overall system performance by proposing optimized request peer selection algorithms for both P2P VoD and P2P live streaming systems.

In P2P VoD, participating peers start playback from the very beginning of a stored video. The playback-points of peers, as well as the amount of video contents/pieces the peers cached, depend on when they join the video session, or their viewing ages. The content buffered by younger peers is a subset of older peers, thus collaborative piece exchange among peers is undermined due to the unbalanced supply and demand. To address this issue, a playback-point based request peer selection algorithm: closest playback-point first (CPF) is proposed. Specifically, when a peer requests a particular video piece, among the set of potential providers, a request is sent to the peer that has the smallest playback-point difference with itself. With CPF, peers with similar content availability are loosely grouped into clusters to maximize the utilization of individual peer’s upload capacity. Extensive packet level simulations show that with CPF, the video playback quality is enhanced and the VoD server load is significantly reduced.

Unlike P2P VoD, P2P live streaming systems have to meet real-time playback constraints, which makes it even more challenging. To better regulate the network traffic and to balance the load among peers, a service response time (SRT) based request peer selection algorithm is proposed. In particular, a peer in the network estimates the service response time (SRT) between itself and each neighboring peer. SRT is measured from when a data piece request is sent until the requested piece arrives. When a peer makes a piece request, the neighbor with smaller SRT and fewer data pieces would be favored. The rationale is: smaller SRT implies excess serving capacity and fewer data pieces suggests fewer potential piece requests received. Extensive packet level simulations show that the traffic load in the network is better balanced, the streaming server load is reduced, and the overall quality of service, measured by playback continuity, startup delay etc., is improved.