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Comcast's usage cap: Is the sky really falling?

Go easy on the overreactions to Comcast's recently announced usage caps. Run the numbers, and you'll see why the cap probably doesn't matter to most users.

When Comcast announced last week that it was instituting a formal usage cap for residential customers--a total of 250 gigabytes of data transfer (uploading plus downloading), as described here--I didn't think much of it, except to be happy they finally defined a critical element of their service guarantee. The previous level of ambiguity was annoying and arguably unlawful, as I described here last October.

Comcast logo

Few Comcast customers will ever consume that much bandwidth, and in fact it's probably several times what Comcast's network can provide to all users anyway. If a large fraction of Comcast's customer base is now encouraged to start sharing its own high-definition home movies on peer-to-peer file-sharing services, network congestion will impose a much lower limit.

But over the weekend I read some of the news coverage and blogger opinions of the cap, and I have to say that some of it is just astonishing. People are making claims and demands that violate the basic rules of mathematics and the laws of physics. It looked like a digital form of mass panic, like the sky was falling.

In this story, the falling acorn was represented by Karl Bode at, whose article announcing the cap (here) was highly speculative but still reasonable.

Blogger Om Malik volunteered for the role of Chicken Little in calling the cap "the end of the Internet as we know it," assuming other carriers follow Comcast's lead.

But Malik's analysis is preposterous. The video-on-demand services Malik claims Comcast is trying to block barely exist yet, so most of us have no experience with them. This isn't the Internet "as we know it," it's the Internet as it might develop if bandwidth were free.

But obviously bandwidth isn't free. Comcast's network wasn't a gift from God. Comcast spent a certain amount of money building it, and it continues spending money to maintain it. Nor does Comcast's network have infinite capacity. Like any other digital-cable network, Comcast's system has intrinsic capacity limits on multiple levels from neighborhoods up to cities.

If some other company institutes a service that relies on dramatically increasing Comcast's network traffic--and therefore the costs of constructing and maintaining its network--why should Comcast have to swallow those costs?

Would Malik let me upload videos to and charge customers for downloads, all without giving him a share of the revenue? Of course not, because he isn't an idiot. He's just not thinking clearly.

(Though Malik went on to use a disgusting excretory analogy to criticize Comcast's announcement--which was, honestly, a very clear, specific, and forthright statement of the company's intentions. What was that about?)

Many other bloggers fell in behind Malik, rushing out to tell the world about the impending disaster.

Running the numbers
But seriously, is there anything to worry about? Let's look at the math. The cap of 250 gigabytes per month works out to a continuous stream of data at over 96 kilobytes per second. Medium-quality digital music works out to 16 kbytes/s, so the cap can't possibly interfere with any amount of music streaming or downloading for personal consumption. Do you listen to Internet radio? That usually operates at even lower data rates, so you're safe. Leave it on 24 hours a day if you like.

Do you watch a lot of videos on YouTube? That's safe too. Even high-quality YouTube videos come in under 90 KB/s, and most of the content there isn't high quality in this sense. If you're on YouTube 24-7, you won't hit the usage cap.

Full standard-definition (SD) video uses a lot more data--usually more than ten times as much as audio. I checked the SD movies at the iTunes Store, for example. The iTunes download of one of my favorite movies, "Blade Runner: The Final Cut," in standard definition is 1:57:28 long and 1.21 GB in size, or 618 MB per hour. At that rate, you could download more than 400 hours of standard-definition TV or movie content in a month without exceeding Comcast's usage cap, even if you do a normal amount of other activity. (Comcast says its median usage for residential customers is less than 3 GB/month.)

There are about 720 hours in a month, so if you spend your whole life watching one new movie after another, you will exceed the cap. Well, at least this is a good reason to spend the usual amount of time eating and sleeping.

Of course, the data rate for HD movies will usually be several times higher than that for SD content. You might only be able to download 100 hours of HD movies per month without raising Comcast's ire.

But c'mon, I know you don't want to watch that many hours of other people's home movies. If you're going to spend that much time watching HD video, you're going to do it with commercial content instead, most likely movies downloaded through Apple TV, Xbox Live, or some similar service. And that means you're going to be spending quite a bit of money, because this content is generally going to cost you $2 to $3 per hour.

If you're doing that, you can afford to spring for Comcast's commercial Internet service, which has no usage caps. It's only around twice the price of residential service--under $100/month. That's a fairly good deal for a service that gives you way more bits per buck than your neighbors are getting.

Still, some people have raised serious objections. CNET's Josh Lowensohn pointed out (here) that online backup services work by transferring large amounts of user data to and from central servers.

In practice, this won't be a problem for all Comcast customers, since these services usually involve much more uploading than downloading and the upload speed for most Comcast customers is just 384 kilobits per second, or less than 125 gigabytes per month, even with uploads running continuously at this speed.

But yes, if you have a service of this type, you'd better keep an eye on it. If you're seeing a daily transfer rate over 6 or 7 gigabytes per second, you'll have to find a way to throttle your bandwidth (often a feature of these services) or upgrade to one of Comcast's commercial Internet packages.

(In the same blog post, however, Lowensohn also made the ridiculous claim that Comcast customers can reach that median monthly usage of 3 gigabytes in "minutes." Although Comcast's best residential service has a peak throughput of 16 megabits per second- giving 3 GB in 25 minutes--there isn't a server in the world that will provide that kind of download speed. So even the fairly sensible people still suffer from a certain level of innumeracy here.)

The facts show that Comcast's usage cap is necessary, reasonable, and high enough that it will never be encountered by most users. Anyone who might be flirting with 250GB/month of usage in the next few years probably ought to be thinking in terms of a commercial account anyway. And after that, as bandwidth gets cheaper and new high-bandwidth services come on line, Comcast (and other ISPs) will inevitably increase the residential usage cap accordingly.

So the sky is safe after all, at least for now. And Chicken Little is still blogging, so I'm sure if he perceives another threat, we'll hear about it.