Just how bad it is Bell Canada's P2P traffic filtering? Not bad at all, so long as you're happy having your 5Mbps DSL link operate at half the speed of a dial-up modem. That's the assertion of a group of small Canadian ISPs that are asking Canada's telecoms regulator to intervene and force Bell to call off its deep packet inspection dogs.

Half the speed of dial-up 

The Canadian Association Internet Providers (CAIP) represents smaller firms that generally purchase wholesale capacity from Bell Canada and resell it under their own brand. When Bell applied its filtering system to this wholesale traffic earlier this year, the operators were outraged, especially as several of them explicitly offered "no throttle" guarantees to customers that they now could not keep.

In documents filed late last week with the Canadian Radio-television and Telecommunications Commission (CRTC), CAIP provided evidence showing that the traffic-shaping system used by Bell limits downstream P2P rates to around 30Kbps during peak times. But those "peak times" aren't just a couple of hours in the evening; they extend from 4:30 PM until 2 AM every day, or 9.5 hours out of each 24.

As CAIP dryly notes, the speed limit "represents a tiny fraction of the 5Mbps downstream data transfer rate" advertised by Bell.

Image courtesy CAIP

Bell's system appears to be nothing if not effective, though. A look at the graph above shows what happens to BitTorrent bandwidth at exactly 2 AM. The image comes courtesy of a TDCNet employee who was downloading a legal copy of Fedora during that time and who saw his bandwidth surge immediately to 450Kbps once Bell Canada let up on the throttle.

CAIP concludes, "It is fair to say that, in general, for up to 10 hours a day, every single day, customers using applications or accessing content that are targeted (either intentionally or collaterally) by Bell's traffic shaping measures are substantially restricted from enjoying the full benefit of the service for which they have contracted."

The reference to collateral damage is further explained in another filing in which CAIP says that Bell Canada's DPI system is far too aggressive and often filters non-P2P protocols. According to CAIP's research, users that start P2P clients are "flagged" for throttling, and once the flag is set, it actually affects everything from SSH to VoIP.

One unnamed CAIP member did an experiment, showing a 500Kbps download speed on SSH transfers and 4.5Mbps downstream using VoIP speed test software. After firing up a P2P client during the peak hours, then shutting it back down, the member found that SSH speed was now reduced to 30Kbps, as was VoIP. The member concluded that this fit with what he had heard, namely that "once a connection has been flagged as a P2P user, all traffic that is not white-listed is throttled."

Bell: We're saving hundreds of thousands from congestion

Not surprisingly, Bell Canada insists that its system is highly accurate, only throttles P2P, and that all complaints it has seen can be chalked up to other network problems. Its comments largely focus on the need for a DPI-based throttling solution, and the company claims that a full 700,000 users would experience congestion problems by next year if Bell did not roll out its solution.

To prove the point, Bell filed a chart showing the history of "network cell loss" on its ATM-based DSL network (the company is currently building a fiber-to-the-node DSL network, but most of its customers still use the older, more expensive ATM technology). Packets are broken up into cells for routing on an ATM network, and when capacity limits are reached and buffers are exceeded, cells will start to be dropped. When this happens, the entire packet becomes unusable and has to be retransmitted. Since 2002, as usage has soared, these loss events have also increased dramatically.