Tracker

• A tracker is a file, located on a server, which lists the holders of each copy of a file available for download. Each entry lists the IP address of the source of the file. The sources are divided into two categories: Seeds and Peers. A seed is the source of a complete copy of a file. A peer holds a partial copy. The protocol used by uTorrent copies files a section at a time. The sections are called blocks and different blocks are copied from different sources. This means an entire copy of a file can be sourced from the owners of partial copies, if all the blocks of a file are distributed among the peers.
  
  

Finding the Tracker

• The uTorrent program lacks one essential element, and that is information about a file to download. A file available to download is called a torrent. The user installs details of a torrent in the uTorrent downloader by opening a meta file in the environment. The meta file contains details of the torrent and the location of the tracker. Once the meta file is opened in the program, uTorrent goes to the tracker, reads the list of Seeds and Peers and contacts the uTorrent program running at that address to request a block of the file from each.
  
  

Purpose

• The tracker system enables the uTorrent network to be completely decentralized. Not only is there no central file server, there is no central tracker server. Several tracker sites around the Internet enable the members of the network to find each other.
  
  

Public and Private

• The sites holding tracker files that uTorrent accesses divide into two categories: public and private. The pubic tracker server is usually associated with a directory or search engine where users look for torrent meta files. Private sites are accessed by invitation only and aim to eradicate uploaders who might use the system to transfer viruses or publicity. Some private tracker sites are free to uploaders, but charge a fee to downloaders. In these cases, the site will also hold the torrent meta file, and only allow access to those to subscribing members who have logged onto the system. Public tracker sites charge no fees and do not require user authentication.