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A BitTorrent tracker is a server which assists in the communication between peers using the BitTorrent protocol . A server is a Computer dedicated to providing one or more services over a computer network typically through a request-response routine For other uses of the term see Peer-to-peer (disambiguation For peer-to-peer networks used for file sharing see File sharing BitTorrent is a Peer-to-peer File sharing protocol used to distribute large amounts of Data. It is also, in the absence of extensions to the original protocol, the only major critical point, as clients are required to communicate with the tracker to initiate downloads. Reliability engineering is an Engineering field that deals with the study of Reliability: the ability of a System or component to perform its required Clients that have already begun downloading also communicate with the tracker periodically to negotiate with newer peers and provide statistics; however, after the initial reception of peer data, peer communication can continue without a tracker.

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Trackers and Indexers

A tracker should be differentiated from a BitTorrent index by the fact that it does not necessarily list files that are being tracked. A BitTorrent index is a list of.torrent files (usually including descriptions and other information managed by a website that is available for searching files to download through A BitTorrent index is a list of . torrent files, usually including descriptions and other information. Trackers merely coordinate communication between peers attempting to download the payload of the torrents.

Many BitTorrent websites act as both tracker and index. Sites such as these publicize the tracker's URL and allow users to upload torrents to the index with the tracker's URL embedded in them, providing all the features necessary to initiate a download. To download is to receive data from a remote or central system such as a Webserver, FTP server, mail server or other similar systems

Private trackers

A private tracker is a tracker which restricts who can use it, often by requiring registration of a user account. A common method for controlling registration among private trackers is an invitation system, in which trusted users are given the ability to grant a new user permission to register at the site. Typically invitations, or the codes that are given to prospective users, are granted to users who have uploaded a pre-determined amount, meet specific ratio requirements, and have been registered. Private trackers usually register how much the users upload and download and may enforce a minimum upload-to-download ratio. As a result of the restricted access, their torrents usually offer better availability and speed compared to public trackers where leeching is more common. In Computing and specifically on the Internet, being a leech or leecher refers to the practice of benefiting usually deliberately from others' information

Many private trackers are now implementing Passkeys in the torrent file, which gives each user a specific address to contact in order to get a list of peers. This helps to prevent unauthorized distribution of torrent files from private trackers.

Legal issues

Main article: Legal issues with BitTorrent

In most countries, it is illegal to distribute copyrighted material without the permission of the copyright holder. The BitTorrent protocol's wide use for Copyright infringement has led to legal issues with BitTorrent. Because of their potential to be used in breach of copyright as well as in compliance, many torrent trackers have been the target of cease and desist lawsuits from copyright bodies; this despite the fact that a tracker does not actually host or distribute any copyrighted data itself but rather the user distributing it from his or her local computer. A cease and desist (also called C & D) is an order or request to halt an activity or else face legal action

A complicating factor is that torrent tracking websites operate in a variety of countries, including countries with copyright laws that differ from the country of origin of the copyrighted material, and countries in which different actions may be legal or illegal.

Further complicating factors are that there are many circumstances under which it is legal to distribute copyrighted material - indeed there are currently some experiments at legally selling content that is distributed over BitTorrent using a "secure" tracker system. For instance, copyright holders may choose to allow their content to be distributed for free, using licenses such as the Creative Commons family, or the GPL. Creative Commons (CC is a Non-profit organization devoted to expanding the range of creative works available for others to build upon legally and to share In addition, some countries also have fair use provisions in copyright law, which allow people the right to access and use certain classes of copyrighted material without breach of the law.

Improving tracker reliability

Trackers are the primary reason for a damaged BitTorrent 'swarm'. (Other reasons are mostly related to damaged or hacked clients uploading corrupt data. ) The reliability of trackers has been improved through two main innovations in the BitTorrent protocol:

Multi-tracker torrents

Multi-tracker torrents feature multiple trackers in the one torrent. This way, should one tracker fail, the others can continue supporting file transfer.

Trackerless torrents

The original BitTorrent client was the first to offer decentralized, distributed tracking using a distributed hash table (DHT), making torrents more independent from the tracker. BitTorrent is a Peer-to-peer program developed by Bram Cohen and BitTorrent Inc Distributed computing deals with Hardware and Software Systems containing more than one processing element or Storage element concurrent Distributed hash tables ( DHTs) are a class of decentralized distributed systems that provide a lookup service similar to a Hash table: ( name, Later, Azureus, µTorrent, BitComet and KTorrent adopted this feature. BitComet (originally named SimpleBT client from versions 011 to 0 KTorrent is a BitTorrent client written in C++ for KDE using the Qt user interface toolkit Azureus' "Distributed Database" feature uses its own form of DHT (Kademlia) which is incompatible with the official BitTorrent client's implementation, although most of the other clients support the official DHT implementation. Kademlia is a Distributed hash table for decentralized Peer to peer Computer networks designed by Petar Maymounkov and David Mazières

IPv6 support

One of the options for this HTTP based tracker protocol is the "compact" flag. This flag specifies that the tracker can compact the response by encoding IPv4 addresses as a set of 4 bytes (32bits). Internet Protocol version 4 ( IPv4) is the fourth revision in the development of the Internet Protocol (IP and it is the first version of the protocol to be widely IPv6 though are 128bits long, and as such, the "compact" flag breaks IPv6 support. Internet Protocol version 6 ( IPv6) is an Internet Layer protocol for packet -switched internetworks. Trackers which support IPv6 clients thus currently ignore the compact flag. There have been mentions of a "compact6" flag, but this mechanism has not been adopted yet by the various BitTorrent clients.

The first IPv6 only worked with BitTorrent and is still run by NIIF/HUNGARNET.

Recently SixXS released their IPv6 only BitTorrent Tracker. This tracker has a permanent set of seeds available on high bandwidth links. The . torrents served by this tracker can be submitted to the catalog, the seeds will then automatically start distributing these . torrents amongst each other, ensuring that the seeds have the full file and providing for high speed downloads for clients. This service makes Open Source distributions readily available over IPv6 in a highspeed way. Open source is a development methodology which offers practical accessibility to a product's source (goods and knowledge

See also

External links

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