BitTorrent begins its seismic shift away from TCP

In an effort to ease the burden its traffic puts on the Internet at large, BitTorrent has announced that it'll use uTP, not TCP, as the transport protocol in its next uTorrent client.

Discussion of the switch from TCP to uTP began late last month, and is set to officially begin in earnest with the 1.9 alpha 13582 build. The exodus from what's essentially the Internet's primary transport protocol could change attitudes toward the popular but bandwidth-intensive BitTorrent, and could have an impact on the great debate over net neutrality.

The uTP protocol enables its own traffic to slow down when it's detected that net latency's on the rise, making it kinder to systems struggling under heavy loads.

Simon Morris, BitTorrent's vice-president of product management, characterized the change as an effort to "offer better congestion control than TCP offers, but maintain the same level of performance.... This is great news for users of the internet and even for ISPs as it should mean that people make far more efficient use of Internet bandwidth, but don't over-use it to destruction. If uTP is successful, then Internet congestion due to BitTorrent protocol could become a thing of the past."

A study earlier this year revealed that uTorrent is the net's most popular torrent client, and the second most popular of all peer-to-peer file-sharing programs.

Delay measurement isn't new tech, but in the Internet's early days, it would have been akin to measuring the congestion caused by children walking across an open field. TCP (transport control protocol) became the more popular option because it gives priority to ensuring all transmitted packets reach their target. Though sometimes the system experiences delays, and the random kid may end up spinning around in circles or playing in mud for a while, eventually all errors are corrected and the children get across the field and to their proper homes.

High-bandwidth applications have changed the game -- to our hypothetical field, let's add a whole lot of ants. (Sorry, kids.) Frankly, no one cares about individual ants making it across the field. As long as most do, the field's still useful for ant-purposes.

UDP Torrenting Protocol (uTP) is one of the User Datagram Protocol (UDP) transport options, which skip TCP's careful handshaking and path-establishment techniques in favor of a "stateless," non-error-checking model. With UDP, most of the ants eventually get across the field. When they do, they sort themselves into their various anthills, and if a particular hill is low on ants...well, don't blame the field. (Also, if a service provider chooses for some reason to privilege UDP over TCP, you end up with something analogous to the ants swarming the children, but that's another story.)

The reason BitTorrent's been such a pain for Internet service providers is that it treats each packet of your high-def Iron Man bootleg as if it were a child, not an ant. Your e-mail packets, those are children -- there aren't many and each is important to the whole. Even Robert Downey Jr.'s mommy doesn't need to receive every single Iron Man packet, because the applications running on her computer will correct for what's missing. (Her boy may be infinitesimally blurry once in a while, but oh well.) uTP embraces BitTorrent's essential ant-nature, as have VoIP, many gaming platforms, and the DNS.

ISPs, as Morris noted, have cause to love the new system; groups opposed to file sharing, not so much. Since "traffic shapers" aren't easily be able to tell one kind of UDP traffic from any other, torrent-blocking packages are apt to be at a loss...at least for a while.

Testers in utorrent's forums seem overall to be seeing good speed improvements; "mojo" gave it a try and said s/he sees "a tremendous impact" on bandwidth, and "nemesis" noted that it's a "very good version...It takes hours until it crash in Vista."