Abstract
Upload utilization is one of the most significant performance metrics in BitTorrent system, whereas there has been no accurate model which is suitable for it yet. For this reason, the delicate relation between some key parameters (maximum concurrent uploads, upload bandwidth, TFT round etc.) in BitTorrent is investigated, furthermore the piece diffusion model and the upload utilization model are proposed. Based on these models, we explore the effect of TFT round for the first time and find that the magnitude of TFT round has a significant influence on the transient stage as well as the end stage. Additionally, we show that when the seed’s upload bandwidth is fully utilized, to achieve optimal performance, each peer’s upload bandwidth should be proportional to its maximum concurrent uploads, and the file size should be large enough compared with the swarm size.
Highlights
BitTorrent is currently the most effective P2P protocol for scalable content distribution, its high efficiency mainly derives from the local rarest first (LRF) policy for piece selection and the tit-for-tat (TFT) policy for peer selection [1]
In order to improve the fairness of BitTorrent, Thommes et al [5] propose a modification in which the number of connections a peer maintains varies with its upload bandwidth instead of a fixed number
In practice, in order to reach the maximum upload utilization, we had better make sure tf is greater than tp, i.e. Eq 6, which implies that the file size should be large enough compared with the swarm size
Summary
BitTorrent is currently the most effective P2P protocol for scalable content distribution, its high efficiency mainly derives from the local rarest first (LRF) policy for piece selection and the tit-for-tat (TFT) policy for peer selection [1]. The high complexity and randomicity of BitTorrent rests above all in its large quantity of parameters, e.g., piece size, maximum concurrent uploads, upload bandwidth, TFT round, number of peers, file size, etc. In previous works which focused on modeling, analysis, and improvement for BitTorrent, there has been no accurate model suitable for the upload utilization, especially when the seed’s upload bandwidth is fully utilized, and the delicate relation between some key parameters has not been revealed either. We explore the effect of TFT round on system performance for the first time and show the delicate relation between some key parameters in order to achieve optimal performance All these models and derived results can be used to further understand the properties of BitTorrent and to optimize the performance in BitTorrent-like systems.
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