Requires centralized trackers to find other users which have the missing pieces, and only then downloads the pieces directly from peers.
Communication with the tracker may happen while the transfer is going on to try and find better peers, but this is optional
Sample magnet URI:
magnet:?xt=urn:btih:1257A35748C96FBAE381B065E300B091CD35EEEF&dn=not+cool+2014+720p+web+dl+x264+etrg&tr=udp%3A%2F%2Ftracker.istole.it%3A80%2Fannounce&tr=udp%3A%2F%2Fopen.demonii.com%3A1337
TODO understand.