Hogging the Trough: The EFF Strikes Back
The art of voodoo network management
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The FCC is to investigate Comcast's network management practices. Last month here I gave an expert view on how the EFF, and other campaigners who called for an inquiry, don't understand the problems. Now Peter Eckserley, a copyright academic at the EFF, has responded to my article. Let's recap the story first.
To avoid congestion on its cable network, Comcast uses a technique to throttle uploads for BitTorrent users; BitTorrent downloads continue to proceed smoothly. Net Neutrality campaigners leapt onto the issue, insisting that Comcast's methods are illegitimate.
Comcast has little choice but to do what they're doing, given the three problems BitTorrent causes for their network - and their customers who don't use BitTorrent.
The first is the nature of BitTorrent itself. BitTorrent's behavior on the Comcast network is like a glutton at an all-you-can-eat buffet who insists on planting himself at the trough, preventing others from getting to the food. This causes multiple problems for DOCSIS cable networks, which caused Comcast's network managers to throttle uploads under high-load conditions (but not prohibit them outright) using a technique called Reset Spoofing.
The EFF has a preferred way of dealing with this, random packet drop. For EFF this is the One True Method of traffic management. But as I've explained to Eckersley both in print and over the phone, the problems BitTorrent causes can't be healed by random packet drop.
Packet drop would work with the regular diner who takes a plateful and moves on, but not with this super-hungry dude.
(I don't attribute malicious intent to BitTorrent's designer Bram Cohen; software often has bugs, even when it wasn't born in Redmond.)
But the EFF soldiers on, its honor now at stake.
Hogging the pipe
The EFF simply dismisses the Denial-of-Service-like effects of BitTorrent handshakes, in which a given Comcast customer's PC can become quite attractive to BitTorrent downloaders because of its favored position in the Tracker's list.
Eckersley correctly noticed that I gave an incorrect reason for this positioning: it's not because of response time, as I said, it's because of the Comcast-resident system's possession of rare file parts, which is even worse. Watch BitTorrent in operation and you'll see cycles of high popularity come and go. It's immune to packet dropping; a connect request comes into the Comcast network, and the user's system responds immediately, regardless of congestion, TCP window sizes, or load.
This highlights a design flaw in the Internet's reliance on TCP packet drop to control congestion generally; packet drop only slows traffic on established streams, not on sessions in the process of becoming established or on non-TCP streams.
Another, more persistent problem that the EFF dodges has been explained by Professor Jim Martin of Clemson University, the world's leading expert on TCP/BitTorrent interaction, and it's simple enough that a copyright expert can certainly grasp it if he wants to.
Residential networks, Comcast's being no exception, are designed on the assumption that users do more downloading than uploading. BitTorrent strives for a symmetric interchange of data, offering as much (or slightly more) in the upload direction as in the download direction. Hence, a small number of BitTorrent sessions will exhaust the network's upload capacity long before it's stressed in the download path. Professor Martin's paper, Assessing the Impact of BitTorrent on DOCSIS Networks [PDF, 450kb] predicts that fifteen BitTorrent sessions significantly slow down web browsing for the neighbors.
The web response time statistic increased from a value of 0.25 seconds when no BitTorrent users were active to 0.65 seconds when 15 BitTorrent users were active. This suggests that 15 BitTorrent users can cause a drop in performance by a factor of 2.5. When the number of BitTorrent users exceeds 30 performance degrades beyond the 1 second metric threshold.
Eckersley is certainly familiar with Martin's work, as he cites him in his original "research" on BitTorrent and Comcast.
An additional problem arises from BitTorrent's tendency to punish users on fast connections with greater traffic loads. Even though Comcast limits upstream traffic to 384kbit/s, a small fraction of its basic 4Mbit/s download rate, upstream traffic moves considerably faster on its network than it does on a standard DSL connection.
Consequently, BitTorrent downloaders will gravitate to peers on Comcast over those on DSL through their own performance assessment.
COMMENTS
Throttle Away Comcast
I am a Comcast customer in the U.S. I noticed some time ago, while using Transmission, that I was suddenly unable to upload to peers the Torrents I'd downloaded. I switched torrent clients and that solved the problem (at least for the moment). I read this piece with much interest. The argument is absolutely sound. P2P traffic has to slow down any network used. It's why the Onion Network developers ask the P2P traffic be kept off of that resource; it simply can't handle the load.
Given the validity of the fact that a certain kind of traffic slows down the network, the problem is this: Comcast sells a product by touting its speed levels. If one visits the Comcast page for US customers, one reads, "Stop crawling the web and start burning rubber with scorching speeds up to 4 times faster than 1.5 Mbps DSL, up to 7 times faster than 768 Kbps DSL, and up to 100 times faster than 56 Kbps dial-up!" Under the Terms, one reads: "Actual speeds may vary and are not guaranteed. Many factors affect speed." Ok. Caveat emptor. They'll do their best to get my service up to those minimums. In testing my connection, however, I have never reached an upload speed anywhere near Comcast's advertised maximum. My upload connection always hovers around 360 Kpbs.
Finally, nowhere is the Terms of Service on Comcast's website does the company state that it will shape its bandwidth, and/or interfere with the software users choose. U.S. law says Comcast may not shape its bandwidth, and must remain neutral is handling various kinds of traffic. The fact that the company was "caught" shaping traffic and then proceeded to lie about it resulted in the FTC's intervention. Comcast officials lied because what they did in response to Bit Torrent's unanticipated and extensive use of its network was to break the law and kill the traffic. It was plainly stupid, at best. I throttle my Torrent speeds voluntarily; I know others do, as well. It's a network, not a trough.
I don't think there's a simple answer to this dilemma. Using the US Mail to commit a crime is a felony. However, clerks may not open your letters at the Post Office to determine whether you are breaking the law. P2P software enables users to break copyright laws in various countries; Comcast is abetting this, and has come under tremendous pressure from those agencies that guard various copyrights. In my opinion, Comcast is between a rock and a hard place.
I am waiting for RIAA and MPAA to start offering companies like Comcast money to block P2P traffic. Paying network providers would be infinitely less expensive and less repugnant than suing college students and other individuals.
Technology advances
ISPs seriously needs to focus on increasing and improving on their network speeds, reliability and customer relations. Investing time and money in throttling services just isn't the answer. I can see a decade ago when web surfing meaunt little more than sendimng an email or loading web pages. Technology has evolved. We are a multi-media world now. Wasting precious resources on limiting what your customers can do is pathetic. Many other countries, Sweden, as an example, offer virually unlimited bandwidth to their people. Japan might be another example. These countries and many other have the foresight and vision to look ahead, not to point fingers at one application, like bittorrent and spend precious time and money to limit people's access.
Truth in advertising...
Richard said: "1. Comcast doesn't advertise an unlimited service, their Terms of Use say you can't run file servers from a standard residential account. BitTorrent running as a seeder is in the category of prohibited applications."
Until 2004, they absolutely did advertise the service as "unlimited". They don't any more, but they also don't tell you that there is, in fact, a limit, because they don't have one. They have a nebulous soft limit, which is whatever the hell they say it is.
Also, their Terms of Use basically states that you give them money and they don't have to provide you with anything at all. Not one byte of data. Heck, their acceptable use policy even prohibits you from downloading porn... which is like 80% of the network, you know.
Like all Terms of Use policies, it's a complete joke. It's basically their fallback position. "We canceled your service because of this policy" is easier to say than "We canceled your service because you're costing us more money than you're making us, thanks to our complete lack of a business plan and reasonable pricing. We like to market things we cannot provide, so as to draw in all the suckers willing to overpay for what they get. Good job, eh?"
While I understand your argument about them controlling their network, there are acceptable and unacceptable ways to do that, and spoofing packets is *never* acceptable. Not that it helps them, of course, because every Comcast user is simply using encryption on their BitTorrent sessions now, which they don't reset because they cannot recognize them anymore.
Bottom line:
If they offer me a speed instead of a limit, then I will adhere to that speed and not to a limit. If they sell me 4 megs down and 384 up, then by god I should get 4 down and 384 up, period. 24/7. All the time. If they cannot provide that, then they damn well should not have sold it to me. If they actually provided what they *claimed* to provide, then they wouldn't be in this mess. If they can't provide it, then they cannot claim it. Truth in advertising is the law, and I really truly hope that the FTC bitch slaps Comcast for their false advertising.
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