P2P

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.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 invite system, which is a system where trusted users are given the ability to grant a new user permission to register at the site. Typically invites, 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.