BitTorrent tracker: Difference between revisions

A BitTorrent tracker is a server which assists in the communication between peers using the BitTorrent protocol. 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. (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.)

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). 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.

Many torrent trackers have been the target of cease and desist lawsuits from copyright bodies, despite the fact that they do not actually host any of the copyrighted data themselves. Some torrent tracking websites are operated in countries with copyright laws that differ from the country of origin of the copyrighted material.

In many countries (including the United States of America), it is illegal to distribute copyrighted material without the permission of the copyright holder. Of course there are many circumstances under which it is legal to distribute copyrighted material. 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. In addition, there are currently some experiments at legally selling content that is distributed over BitTorrent using a "secure" tracker system.

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

There are two incompatible 'trackerless' BitTorrent transfer (aka. decentralized tracking) methods: DHT-based implementations, and Azureus's 'Distributed Database'.

The term 'trackerless' is something of a misnomer, as decentralized or distributed tracking essentially treats every peer in the swarm as a tracker. Original BitTorrent was the first client to offer decentralized tracking through its DHT method. Later, Azureus, µTorrent and BitComet adopted this feature, although Azureus's method of implementation is incompatible with the DHT offered by all other supporting clients.

BitCometTracker - C++(?), Windows Only Extended BitTorrent client and Tracker (XBTT) - Windows/Linux

Blog Torrent - Supports webseed, does not require MySQL(?). ABANDONED Broadcast Machine - Successor to Blog Torrent, Focuses on Torrentcasts BT phpTracker Plus - Coded from scratch; lightweight Btittracker - A frontend for phpBTTracker ByteStats Tracker - External scrape support, installation script. ABANDONED PHP Nuke BitTorrent Module - BitTorrent tracker module for the popular PHPNuke CMS phpMyBitTorrent - Successor to the PHPNuke Tracker Module, this is a standalone tracker with many features PHPBTTRACKER - Installer, MySQL. ABANDONED PHPBTTRACKER+ - Tracker based on PHPBTTRACKER. Many extra features PHPBTTracker-Admin - Another tracker based on PHPBTTRACKER, also with many additional features.

(Inserting list here as of 21:50 MST July 9)

• BitTorrent
• Bram Cohen
• BitTorrent client
• Distributed hash tables
• Share ratio
• UDP tracker
• BNBT - C++ port of the original BitTorrent tracker written in Python by Bram Cohen