BitTorrent is a protocol of transfer of information Poste at station (P2P) through a Data-processing network developed by Bram Cohen. The protocol was conceived in April 2001 and set up at the summer 2002 by the programmer Bram Cohen, and is henceforth maintained by the BitTorrent company.

The BitTorrent protocol leaves the following report:

  • When information is on a data-processing Serveur single, more it is required, less it is accessible (by saturation of the waiter).
  • One reverses this tendency if one allows each data-processing Client having downloaded information to become at once waiter in his turn.

Advantages

BitTorrent is a method to widely distribute great quantities of Données by distributing the inherent load as regards Matériel, Hébergement Internet and Band-width when, in the traditional model, it falls on the only original distributer. With the place that this last serf each recipient, with BitTorrent the customers themselves are used the data for the new recipients. Thus the cost and the load of the distribution of the data are considerably reduced; the protocol gets at the same time a Redondance against the material problems and reduces the dependence with regard to the original distributer.

This “network” uses the techniques most led for the use of P2P, namely: the remote loading Poste at station since various “pars” ( peer ) for the same file (called “multisourcing”) and parcelling out of the file in blocks, which constrained step to await a user having the adjacent blocks with the already downloaded part (for example if the file is composed of 10 blocks, if one already blocks 1,2 and 3, one has is not obliged to await block 4 to continue, and one can very receive block 9 or any other block).

Moreover, the validity of the data is implicitly guaranteed (if the file is corrupted, it is that it was it in the beginning, or that it was it on the computer downloading it (defective Random access memory, for example, but to in no case during the transfer of information). The corrupted blocks are invariably rejected.

This network shows all its effectiveness when it there has much of users, since the more there is world which downloads, the more there is world which divides, and one should not wait in a virtual file to start, it is direct (in condition, that goes from oneself, which at least a person divides the desired file).

Compared to other systems P2P, this system with the advantage of creating a kind of virtuous circle at the time of the division of the files. Indeed, as soon as parts of the desired file are downloaded, they are available for the other users. Moreover one system of “reward” allows to receive more if one gives more. That which gives little or at all will receive much less others.

This system strongly benefits from the increase in the band-width available in “upload”, i.e. in sending of data, connections network.

Disadvantages

For those of which connection to the Web is calculated and invoiced with the band-width ( bandwidth ), consumption ( upload and download ) can in certain cases double or triple.

The band-width in upload can be saturated if the software used to download on the BitTorrent network is not configured correctly (according to the capacities of connection to Internet of the user): that involves an important deceleration of all connections to Internet in progress. Remote loadings HTTP and ftp can almost stop and the reading of radios/tv Internet can be jerked even impossible. Software of cat (live messenger, gaim, IRC,…) are not affected because of the low volumes of data which they have need to transmit towards and since Internet.

To avoid the saturation of the upload, it is recommended to configure the customer so that it uses only 80% of the band-width available in upload. Examples:

  • 6 ko/s maximum for a connection 56K (capacity in upload: 8 ko/s);
  • 12 ko/s maximum for a symmetrical connection ISDN 128 ko/s or ADSL xxx/128 (capacity 16 ko/s);
  • 51 ko/s maximum for a connection ADSL xxxx/512 (capacity 64 ko/s);
  • 102 ko/s maximum for a connection ADSL xxxxx/1024 (capacity 128 ko/s).

A person who divides little will receive also much less other users. There exist however customers based on the BitComet engine not respecting completely the BitTorrent protocol; these customers allow to receive many data while dividing little (while making accept the others peers which they already sent of the data). Because of their non-observance of the protocol, these customers slow down potentially the network BitTorrent, it thus agrees not to use them.

Newcomers

The BitTorrent protocol exploits the principle " one lent for a rendu" , supporting the exchange of information between machines which already cooperated in the past. This can involve a difficult starting of a newcomer when all the other machines have already almost the totality of the file.

Availability

The operating process observed of BitTorrent suffers from a major handicap: at the beginning of the setting of availability of a file, much of sources are available to download it, especially if it popular or is awaited for a long time; but with time, it becomes less and less divided, and thus less and less available to the remote loading, which leads to “dead” of the torrent. Thus, it is rare that a torrent is active during more few months, even a few weeks or even a few days.

To cure that, the customers now propose to leave the “opened” torrent, once downloaded. That becomes a pure source then and cures this disadvantage.

The limit with this reasoning is like always the place available on the hard drives and other storage systems on line.

Use

It is often necessary to use a software dedicated to download the files whereas an accessible file on a Web site does not require anything more than the navigator to repatriate it.

Note: The navigator Web Opera 9 includes a customer BitTorrent, the files torrent being treated in a transparent way. Some Plugin S of the navigator Mozilla Firefox also make it possible to add this functionality to the navigator. Just like the version 1.80 of the Flashget downloader which also takes charges this type with it of file. Also, of many software p2p (Shareaza, LimeWire…) contain this function.

The first configuration can be tiresome, if one does not have some minimal concepts of Data-processing network, Adresse IP, Pare-feu (Firewall) and concept of software Port, for example. The majority of the recent software customers allow an automatic configuration according to the characteristics of the surrounding network, but certain customers/modems require a specific configuration. For example, to download at an optimal speed by using a Box, it is in general necessary to redirect manually (in the configuration of the router mode of the " Box") the port used by the BitTorrent customer towards the IP (on the lan) of the computer on which the customer turns. In the case of a customer using a port randomly in a preset beach (as BitTornado which uses by defect a port randomly among ports 10000 to 60000), it is necessary to redirect the whole beach towards the computer making turn the customer. That can pose problem when another computer on the same lan uses a port included/understood in this beach.

Research

To find the torrents, it is necessary to go on IRC or Web sites counting them, like Mininova, Snarf-It, Isohunt… An search engine is also in place.

Vocabulary

Availability/ availability: (also called “distributed copies”) quantity of complete copies of the file available. A peer which is connected with a fraction of file adds this fraction to the availability (if no other has already this part of the file). Each seed adds 1,0 to this number, since it has the totality of the file. Thus, a peer with 65,3% of a downloaded file increases the availability of 0,653. If two peers downloaded each one the same half of a file and that they are joined by a seeder (sower), the availability amounts to 1,5.

Leecher : A “leech” ( leech in English) is a customer wishing to download the file, but not having it entirely. This term has also a pejorative direction to qualify those which download without n the other hand sending file on the network. During the first appearance of a torrent, there are only few sources (seeds) and much leeches (leech).

Peers : Users being able to transmit whole or part of the file (seeders or leechers having part of information).

Scrape : The Bittorrent customer (see customers using the network BitTorrent) begin with a scrape , which consists in requiring of the tracker information on the full number of sources ( seeds ) and of leeches ( leech ). This number will be generally posted between brackets.

Seed : A seed ( seed in English) is a customer dividing a complete file.

Share Ratio : Proportion enters the number of data sent, shared (upload) and the number of received data ( download ). In a utopian world, each and everyone using this service should have a ratio of 1:1, which indicates that there were as many data sent received. In this way the remote loadings are fast and effective for all.

Superseed : Seed which tries to minimize the quantity of data that it sends until a leecher obtains the totality of the files of the torrent and becomes thus an additional seeder. This function should be used only when that there is one seeder, or very little of them, available for a torrent, and that these seeders has relatively limited capacities of upload. The operation consists in not stating to have any part of the file. When the customers connect themselves, super-seeder the formless one that it has a new part that nobody has. It transmits the part in question and will not transmit any new part of the file as long as it will not have received confirmation which the part was again transmitted. In this manner, the customers in mode superseed send only the pieces which were never yet sent, and make sure of their good diffusion by, and among, the leechers.

Swarm : All the peers (including the seeds ) which divide the same torrent are called a swarm . For example, six peers and two seeds form a swarm of eight units.

Torrent : According to the context, a torrent can mean either file of Métadonnée S .torrent, or any file described by him. The file torrent contains metadata relating to the files which it makes downloadable, including their names, sizes and checksums of all parts of the torrent. It also contains the Adresse IP of a tracker which coordinates the communication between the peers of the swarm (swarm).

Tracker : A traquor is a waiter which knows permanently which seeds and which peers is in the swarm (the swarm). The customers send information regularly to him. In exchange, they receive information on other customers to which they can be connected. The traquor is not directly implied in the transfer of information and does not have a copy of the file.

Web Seeding : To use a Web server like seed . Using scripts php, of a modification of the torrent one can pemettre with a Web server of seeder a torrent. This functionality was integrated in the customers Mainline, Azureus, and Bit-tornado.

Copyright

Although the BitTorrent protocol was Open source to the release of version 6 of the official customer (µTorrent), there remains problems involved in the Copyright. Certain organizations of monitoring of the royalties are interested of close with the sites providing the trackers because those are often means of distribution of laid off files (musics, films, etc).

Motion Pictures Agency off America (MPAA) in particular, brought multiple referring lawsuits towards various sites of the files .torrent because of the great number of files illegally distributed thus. One of the most recent businesses relates to the site ThePirateBay.org, continued by the Swedish police force and the MPAA (beginning of the business May 31st, 2006, always in progress).

To download a laid off video file, image or audio is an offense and more still, to distribute it to large scales is liable to heavy fines and prisons (see DADVSI). But the files .torrent are not strictly speaking these laid off files, they are only one means of downloading them. Thus, in theory, the sites gathering of the trackers are not " outlaw ".

The legality of the detention of files .torrent allowing the downloading files under copyright remains still rather fuzzy, the MPAA and the other organizations of protection of royalties having attacked in justice of the sites as various as of the shelterers of files or the search engines for torrents while not lodging (TorrentSpy 2/27/2006).

Attention, the legislation depends on the country, for example in Switzerland it is legal to download a film, which is not the case in France.

BitTorrent 6 brought a major change to the level of the license: indeed, until there, the associated program and the protocol were Open source. The license of use was modified, and the protocol will not see any more its code published, even if it is possible to obtain a SDK in order to continue the development of third software

List the most popular customers

BitTorrent being a free protocol , many alternative programs could be developed. Among most popular, one can quote:

  • ABC, Windows, GNU/Linux
  • AllPeers, extension of Firefox, Windows, GNU/Linux, Mac OS X
  • Azureus developed in Java (Vuze), Windows, GNU/Linux, Mac OS X
  • BitComet, Windows
  • BitSpirit, a customer for Windows
  • BitTornado, Windows, GNU/Linux
  • Bits one Wheel for Mac OS X.
  • BitTorrent: a simple and basic customer, a customer for the environment GNU/Linux
  • Creatorrent an extra-light customer to create a torrent in mode comforts, GNU/Linux
  • Deluge, encrypted BitTorrent customer under GNU/Linux
  • KTorrent, a customer for the environment KDE, GNU/Linux
  • LimeWire, Windows, GNU/Linux, Mac OS X
  • MLDonkey, a multiprotocol customer, Windows, GNU/Linux, Mac OS X
  • MonoTorrent is a light ultra customer and multi-platform (mono)
  • µTorrent (microtorrent) an extra-light customer but who is not any more open-source Windows
  • Opera (continuation Internet) since his version 9 for Mac OS X, GNU/Linux and Windows
  • Rtorrent an extra-light but completely complete customer in mode comforts, GNU/Linux
  • Shareaza, Windows
  • Transmission for Mac OS X, GNU/Linux and BeOS
  • Xtorrent for Mac OS X.

The official customer, quickly exceeded in market shares by the rival software above, bears the same name as the protocol itself, BitTorrent.

At the beginning of December 2006, BitTorrent Inc., the company created by Bram Cohen, the inventor of BitTorrent, and Ashwin Navin old of Yahoo!, announces the acquisition of the software owner µTorrent. This software replaces the former free customer then BitTorrent as “an official customer”.

BitTorrent Entertainment Network

BitTorrent opens on February 26th, 2007 a paying platform of remote loading: BitTorrent Entertainment Network. If the prices charged are relatively relatively low (3,99 $ for a recent film) compared to other platforms of this type, BitTorrent Entertainment Network suffers on the other hand because of proposing its films only for the hiring, and protected by DRM. The studios having signed an agreement of diffusion are for the moment:

Sources

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