The BitTorrent mechanism effectively spreads file fragments by copying the rarest fragments first. We propose to apply a mathematical model for the diffusion of fragments on a P2P in order to take into account both the effects of peer distances and the changing availability of peers while time goes on. Moreover, we manage to provide a forecast on the availability of a torrent thanks to a neural network that models the behaviour of peers on the P2P system. The combination of the mathematical model and the neural network provides a solution for choosing file fragments that need to be copied first, in order to ensure their continuous availability, counteracting possible disconnections by some peers.
Several studies have analysed the behaviour of BitTorrent systems from the point of view of fairness, i.e. how to have users contribute with contents that can be uploaded by other users, levelling the amount of downloads with that of upload. Fewer works have studied the problem of unavailability of contents in P2P BitTorrent networks. @cite_12 , authors proposed to order peers according to their uploading bandwidth, hence when providing contents the selection of peers is performed accordingly. One of the mechanism proposed to increase files availability has been to use multi-torrent, i.e. for ensuring fairness, instead of forcing users stay longer, they provide their contribution to uploaders for fragments belonging to different files @cite_18 . Similarly, in @cite_3 authors show that by using multi-torrent availability can be easily increased, and confirm that fast replication of rare fragments is essential. Furthermore, bundling, i.e. the dissemination of a number of related files together, has been proposed to increase availability @cite_6 .
@cite_18 @cite_3 @cite_6 @cite_12
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Existing studies on BitTorrent systems are single-torrent based, while more than 85 of all peers participate in multiple torrents according to our trace analysis. In addition, these studies are not sufficiently insightful and accurate even for single-torrent models, due to some unrealistic assumptions. Our analysis of representative Bit-Torrent traffic provides several new findings regarding the limitations of BitTorrent systems: (1) Due to the exponentially decreasing peer arrival rate in reality, service availability in such systems becomes poor quickly, after which it is difficult for the file to be located and downloaded. (2) Client performance in the BitTorrent-like systems is unstable, and fluctuates widely with the peer population. (3) Existing systems could provide unfair services to peers, where peers with high downloading speed tend to download more and upload less. In this paper, we study these limitations on torrent evolution in realistic environments. Motivated by the analysis and modeling results, we further build a graph based multi-torrent model to study inter-torrent collaboration. Our model quantitatively provides strong motivation for inter-torrent collaboration instead of directly stimulating seeds to stay longer. We also discuss a system design to show the feasibility of multi-torrent collaboration. BitTorrent suffers from one fundamental problem: the long-term availability of content. This occurs on a massive-scale with 38 of torrents becoming unavailable within the first month. In this paper we explore this problem by performing two large-scale measurement studies including 46K torrents and 29M users. The studies go significantly beyond any previous work by combining per-node, per-torrent and system-wide observations to ascertain the causes, characteristics and repercussions of file unavailability. The study confirms the conclusion from previous works that seeders have a significant impact on both performance and availability. However, we also present some crucial new findings: (i) the presence of seeders is not the sole factor involved in file availability, (ii) 23.5 of nodes that operate in seedless torrents can finish their downloads, and (iii) BitTorrent availability is discontinuous, operating in cycles of temporary unavailability. BitTorrent, the immensely popular file swarming system, suffers a fundamental problem: unavailability. Although swarming scales well to tolerate flash crowds for popular content, it is less useful for unpopular or rare files as peers arriving after the initial rush find the content unavailable. Our primary contribution is a model to quantify content availability in swarming systems. We use the model to analyze the availability and the performance implications of bundling, a strategy commonly adopted by many BitTorrent publishers today. We find that even a limited amount of bundling exponentially reduces content unavailability. Furthermore, for swarms with highly unavailable publishers, the availability gain of bundling can result in a net improvement in download time, i.e., peers obtain more content in less time. We empirically confirm the model's conclusions through experiments on PlanetLab using the mainline BitTorrent client. In this paper, we develop simple models to study the performance of BitTorrent, a second generation peer-to-peer (P2P) application. We first present a simple fluid model and study the scalability, performance and efficiency of such a file-sharing mechanism. We then consider the built-in incentive mechanism of BitTorrent and study its effect on network performance. We also provide numerical results based on both simulations and real traces obtained from the Internet.