In the mid-80s, the internet was subject to a phenomenon called “Congestion Collapse” that frequently made it unusable. Congestion Collapse (also known as “internet meltdown”) came about because the system that was designed into IP to notify systems of network congestion, “Source Quench” messages, didn’t work when the network was too congested to handle additional traffic. So an algorithm was developed - the Jacobson Algorithm - to slow down the rate at which TCP offered traffic to the network when it was evident that routers weren’t able to handle the traffic load. While Jacobson is highly inefficient – often causing network links to cycle between 50 per cent to 75 per cent of capacity – it does in fact lead to stability, a much more important goal than efficiency.
The ISPs' dilemma
ISPs which throttle users based on raw traffic volume (as the new Comcast system will do) are protected from the effects of the massive use of aggressive UDP inside their networks. And they should be, as these private networks aren’t internets in and of themselves. The damage is going to appear inside the core internet links connecting ISPs, which will become much less responsive to load management.
One rational response is to make UDP the prime candidate for packet discard. When five per cent of users consume half the network’s resources and block access to 75 per cent of its total capacity, it makes sense to target them for throttling. But such throttling will utterly destroy VoIP.
(Note: in principle, VoIP can be distinguished from P2P over UDP, but only by non-politically correct means such as Deep Packet Inspection. Nor is it consistent with the net neutrality laws proposed in the US and the EU forbidding discrimination based on protocol type, source, or destination.)
uTorrent’s net-killing feature is a slap in the face to the very regulators who’ve sanctioned ISPs in the name of this “innovative new application”: it bites the hand that’s fed it with immunity from rational management. And it also gives the lie to the internet Utopians who’ve claimed that internet users manage shared facilities so well that throttling isn’t necessary inside the network. Such idealism is simply a prescription for the return of internet meltdown, this time with a vengeance.
The internet evolved as a gentleman’s system in the comfortable confines of the ivory towers of academe, but now that it’s an essential part of daily life for more than a billion people, the time has come to get realistic about its management. Some of the people who use this system are spoiled children with no more concern for the greater good than junkies looking for their next fix. They can’t be allowed to spoil it for the rest of us, and the only practical means to prevent their doing so is to unleash effective management upon them.
The best way to ensure that uTP doesn’t kill the internet is to throttle it at the source, and any law that stands in the way of ISPs exercising that level of management is deadly to the internet. We can thank the uTorrent developers for reminding us of that salient fact.
Richard Bennett is a network architect and occasional activist in Silicon Valley. He wrote the first standard for Ethernet over twisted-pair wiring and contributed to the standards for Wi-Fi and the Ultra-Wideband wireless networks. His 11-year-old blog is at bennett.com.