The UDP tracker is a high-performance low-overhead BitTorrent tracker protocol. It uses the stateless (UDP) for data transmission instead of the HTTP protocol (over ) regular trackers use. The data is in a custom binary format instead of the standard bencode algorithm BitTorrent uses for most communication.
URLs for this protocol have the following format: udp://tracker:port.
The UDP tracker is better optimized and puts less strain on the tracking server. Neither tracker has any effect on transfer speeds.