A key design change in P2P applications by leading BitTorrent software authors will cause havoc for any users needing to wring high performance out of their networks.

In reaction to Bell Canada’s system for allocating bandwidth fairly among Internet users, the developers of the P2P application, uTorrent, have decided to make the UDP protocol the default mechanism for the transfer of data files.

Previously reserved for real-time data transfer, UDP has long been used to exchange tracker information (the addresses of the computers where files could be found) on the P2P network. However, the latest release uses it in preference to TCP for the transfer of all files.

uTorrent is owned by BitTorrent Inc and it won’t be long before other BitTorrent implementations follow it’s lead. This will place the burden of reducing network load during heavy traffic periods squarely on the shoulders of TCP uses (most importantly web browsing and video streaming).

“BitTorrent is essentially biting the hand that feeds,” said Bruce Mills, Joint CEO of 3W Consulting Contracting & Recruitment Pty Ltd. “This decision capitalises on lenient Internet regulations governing the use of UDP.”

“It is likely to have an enormous knock-on effect on Internet performance for all users — especially for those using time-sensitive data transfer applications such as gamers, VoIP and videoconference users.”

“P2P is estimated to account for almost 50% of Internet traffic today,” said Mills. “When this traffic moves over to UDP and becomes immune to congestion control, the remaining half will be left to struggle along at roughly one quarter of the bandwidth is currently enjoys. This equates to 95% of Internet users using half the raw bandwidth with half the efficiency – a recipe for disaster.”

Return of the 80s Internet meltdown

UDP was intended to move small amounts of data in applications with a low tolerance for delay (such as VoIP). Currently, it accounts for less than 2% of all Internet traffic. Delay tolerant, bulk data transfers such as the majority of P2P file transfers) are meant to use TCP, which is designed to manage congestion for the Internet’s end-to-end layer.

“If this protocol is rolled out, we are likely to see a return of the 1980s phenomenon known as ‘Congestion Collapse’,” Mills warned.

Also called ‘Internet Meltdown’, it came about because at the time, the Internet was designed to notify systems of network congestion. These ‘Source Quench’ messages did not work when the network became overly congested.

An algorithm, called the Jacobson Algorithm, was developed to slow down the rate at which TCP offered traffic to the network when routers became overloaded with traffic. Despite it’s shortcomings (it is notoriously inefficient and often causes network links to cycle between 50% and 75% of capacity), the algorithm lead to Internet stability — far more important than efficiency.

“The Internet as we know it owes its stability to application developers’ courteous allotment of traffic onto the network,” explained Mills. “uTorrent’s new protocol will see 5% of users consuming half the network’s resources and blocking access to 75% of its total capacity. This flies in the face of the historically genteel approach.”

Altruistic regulations rule out rational management

Private networks, using systems, such as the new Comcast system, which throttle users based on raw traffic volume, are protected from the effects of large-scale use of aggressive UDP. While effects may not be felt within the ISP’s network, core Internet links connecting ISPs will be targeted.

A rational response to BitTorrent’s decision is to make UDP the prime candidate for packet discard and target them for throttling. But this will utterly destroy VoIP.

“In principle, VoIP can be distinguished from P2P over UDP,” said Mills, “but only by employing non-politically correct means (for example Deep Packet Inspection). Unfortunately, net neutrality laws proposed in the US and the EU forbid discrimination based on protocol type, source or destination.”

“This new feature is an insult to the regulators who have sanctioned ISPs to go ahead with the P2P application. It serves only to accentuate that Internet users cannot be trusted to manage shared facilities without the need for throttling within networks,” he added.

“Now that the Internet has evolved from its beginnings in academia and become an essential element in the daily life of more than a billion people, it’s time to implement more stringent management.”

“The best way to prevent uTorrent (and other applications) from killing the Internet for all of us is to control it at the source. Any legislation that prevents ISPs from implementing effective management measures to achieve this should be revisited as a matter of urgency.”