UDP or User Datagram Protocol is built on top of IP, and is used when it is required to send the data packets directly. Unlike TCP, which is a huge bundle of features and data, it is considered a very fine layer on top of IP. Utilizing the feature of UDP, which allows it to be more efficient; a tracker protocol of UDP is used by BitTorrent, which is used to transfer the data in the famous Peer to Peer file sharing. Previously, the data was sent on TCP or HTTP based tracker, which is not in use anymore, because of the overloading of bandwidth on networks. One can see the new URL format on their torrents details as udp://tracker:port.

Advantages of UDP based tracker

An advantage of using this tracker is that it does not overload the tracker server. However, it is not supported by a wide range of BitTorrents client. The reason behind this could simply be the fact that they do not know much about this tracker protocol, or that they do not feel the urge to bring the change. An advantage that HTTP based tracker has on UDP based is that they can inform the users about the stats on the torrent files, like the number of seeders and leechers of the torrent. However, both the torrents have close to no effect on the transfer speed of the data.

One of the advantages that UDP based tracker has over the HTTP base is overhead. There are additional overheads in the Ethernet, IP, TCP and HTTP later, which significantly consumes the data transfer bandwidth. Around 10 packets are used in case of 50 peers asking for response, consuming 1206 bytes. The amount of traffic and users of Peer to Peer file sharers is significantly huge, which in turn takes the network traffic to critical levels. UDP based trackers can easily reduce the number of packets or overhead being used. This tracker only uses 4 packets and uses only 618 bytes, which is almost 50% less traffic. Even though, the number of bytes reduced is not that high, but if one cumulates all the used traffic, the numbers are quite significant. The tracker is also preferred because it does not require and complex algorithm and the tracker code are quite simple.

Is it the perfect alternative?

Although, it is considered to be a great alternative, however, there are certain scenarios on which questions are being raised. One certain example would be the danger of spoofing. There are no more than 4 packets used for response, as mentioned above. This means that there is a good chance of the data or the address of the source getting spoofed. This is however, taken care of by the tracker itself, where it keeps a lookout on the connection id. Conditions like sniffing of the network can surely affect its reliability, but such cases are seen in TCP based tracker as well. Despite some of its disadvantages, the UDP based tracker is being used by many BitTorrent clients such as 1337x, Ktorrent, Flashget, Vuze, etc.