text: Peer-to-peer (P2P) overlay networks such as BitTorrent and Avalanche are increasingly used for disseminating potentially large files from a server to many end users via the Internet. The key idea is to divide the file into many equally-sized parts and then let users download each part (or, for network coding based systems such as Avalanche, linear combinations of the parts) either from the server or from another user who has already downloaded it. However, their performance evaluation has typically been limited to comparing one system relative to another and typically been realized by means of simulation and measurements. In contrast, we provide an analytic performance analysis that is based on a new uplink-sharing version of the well-known broadcasting problem. Assuming equal upload capacities, we show that the minimal time to disseminate the file is the same as for the simultaneous send receive version of the broadcasting problem. For general upload capacities, we provide a mixed integer linear program (MILP) solution and a complementary fluid limit solution. We thus provide a lower bound which can be used as a performance benchmark for any P2P file dissemination system. We also investigate the performance of a decentralized strategy, providing evidence that the performance of necessarily decentralized P2P file dissemination systems should be close to this bound and therefore that it is useful in practice.
  @cite_19: 
  @cite_15: The BitTorrent file distribution system uses tit-fortat as a method of seeking pareto efficiency. It achieves a higher level of robustness and resource utilization than any currently known cooperative technique. We explain what BitTorrent does, and how economic methods are used to achieve that goal. 1 What BitTorrent Does When a file is made available using HTTP, all upload cost is placed on the hosting machine. With BitTorrent, when multiple people are downloading the same file at the same time, they upload pieces of the file to each other. This redistributes the cost of upload to downloaders, (where it is often not even metered), thus making hosting a file with a potentially unlimited number of downloaders affordable. Researchers have attempted to find practical techniqes to do this before[3]. It has not been previously deployed on a large scale because the logistical and robustness problems are quite difficult. Simply figuring out which peers have what parts of the file and where they should be sent is difficult to do without incurring a huge overhead. In addition, real deployments experience very high churn rates. Peers rarely connect for more than a few hours, and frequently for only a few minutes [4]. Finally, there is a general problem of fairness [1]. The total download rate across all downloaders must, of mathematical necessity, be equal to the total upload rate. The strategy for allocating upload which seems most likely to make peers happy with their download rates is to make each peer’s download rate be proportional to their upload rate. In practice it’s very difficult to keep peer download rates from sometimes dropping to zero by chance, much less make upload and download rates be correlated. We will explain how BitTorrent solves all of these problems well. 1.1 BitTorrent Interface BitTorrent’s interface is almost the simplest possible. Users launch it by clicking on a hyperlink to the file they wish to download, and are given a standard “Save As” dialog, followed by a download progress dialog which is mostly notable for having an upload rate in addition to a download rate. This extreme ease of use has contributed greatly to BitTorrent’s adoption, and may even be more important than, although it certainly complements, the performance and cost redistribution features which are described in this paper.
  @cite_23: Keywords: peer-to-peer ; content distribution ; performance ; analysis Reference LCA-CONF-2006-009 URL: http: drops.dagstuhl.de portals index.php?semnr=04201 Record created on 2006-05-18, modified on 2017-05-12
  @cite_5: Recent reports in the popular media suggest a significant decrease in peer-to-peer (P2P) file-sharing traffic, attributed to the public's response to legal threats. Have we reached the end of the P2P revolution? In pursuit of legitimate data to verify this hypothesis, in this paper, we embark on a more accurate measurement effort of P2P traffic at the link level. In contrast to previous efforts, we introduce two novel elements in our methodology. First, we measure traffic of all known popular P2P protocols. Second, we go beyond the "known port" limitation by reverse engineering the protocols and identifying characteristic strings in the payload. We find that, if measured accurately, P2P traffic has never declined; indeed we have never seen the proportion of P2P traffic decrease over time (any change is an increase) in any of our data sources.
summary: With the BitTorrent protocol http: bitconjurer.org BitTorrent protocol.html , for example, when the load on the server is heavy, the protocol delegates most of the uploading burden to the users who have already downloaded parts of the file, and who can start uploading those parts to their peers. File parts are typically @math megabyte (MB) in size. An application helps downloading peers to find each other by supplying lists of contact information about randomly selected peers also downloading the file. Peers use this information to connect to a number of neighbours. A full description can be found in @cite_15 . The BitTorrent protocol has been implemented successfully and is deployed widely. A detailed measurement study of the BitTorrent system is reported in @cite_19 . According to @cite_23 , BitTorrent's share of the total P2P traffic has reached 53 . For recent measurements of the total P2P traffic on Internet backbones see @cite_5 .