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An obscure blogger films his three-year-old daughter reciting the plot of the first Star Wars movie. He stitches together the best parts–including the sage advice “Don’t talk back to Darth Vader; he’ll getcha”–and posts them on the video-sharing website YouTube. Seven million people download the file. A baby-faced University of Minnesota graduate student with an improbably deep voice films himself singing a mind-numbingly repetitive social-protest song called “Chocolate Rain”: 23 million downloads. A self-described “inspirational comedian” films the six-minute dance routine that closes his presentations, which summarizes the history of popular dance from Elvis to Eminem: 87 million downloads.

Video downloads are sucking up bandwidth at an unprecedented rate. A short magazine article might take six minutes to read online. Watching “The Evolution of Dance” also takes six minutes–but it requires you to download 100 times as much data. “The Evolution of Dance” alone has sent the equivalent of 250,000 DVDs’ worth of data across the Internet.

And YouTube is just the tip of the iceberg. Fans of Lost or The Office can watch missed episodes on network websites. Netflix now streams videos to its subscribers over the Internet, and both Amazon and Apple’s iTunes music store sell movies and episodes of TV shows online. Peer-to-peer file-sharing networks have gradu­ated from transferring four-minute songs to hour-long ­Sopranos episodes. And all of these videos are higher quality–and thus more bandwidth intensive–than YouTube’s.

Last November, an IT research firm called Nemertes made headlines by reporting that Internet traffic was growing by about 100 percent a year and that in the United States, user demand would exceed network capacity by 2010. Andrew Odlyzko, who runs the Minnesota Internet Traffic Studies program at the University of Minnesota, believes that the growth rate is closer to 50 percent. At that rate, he says, expected improvements in standard network equipment should keep pace with traffic increases.

But if the real rate of traffic growth is somewhere between Nemertes’s and Odlyzko’s estimates, or if high-definition video takes off online, then traffic congestion on the Internet could become much more common. And the way that congestion is relieved will have implications for the principles of openness and freedom that have come to characterize the Internet.

Whose Bits Win?
The Internet is a lot like a highway, but not, contrary to popular belief, a superhighway. It’s more like a four-lane state highway with traffic lights every five miles or so. A packet of data can blaze down an optical fiber at the speed of light, but every once in a while it reaches an intersection where it has the option of branching off down another fiber. There it encounters a box called an Internet router, which tells it which way to go. If traffic is light, the packet can negotiate the intersection with hardly any loss of speed. But if too many packets reach the intersection at the same time, they have to queue up and wait for the router to usher them through. When the wait gets too long, you’ve got congestion.

The transmission control protocol, or TCP–one of the Internet’s two fundamental protocols–includes an algorithm for handling congestion. Basically, if a given data link gets congested, TCP tells all the computers sending packets over it to halve their transmission rates. The senders then slowly ratchet their rates back up–until things get congested again. But if your computer’s transmission rate is constantly being cut in half, you can end up with much less bandwidth than your broadband provider’s ads promised you.

Sometimes that’s not a problem. If you’re downloading a video to watch later, you might leave your computer for a few hours and not notice 10 minutes of congestion. But if you’re using streaming audio to listen to a live World Series game, every little audio pop or skip can be infuriating. If a router could just tell which kind of traffic was which, it could wave the delay-sensitive packets through and temporarily hold back the others, and everybody would be happy.

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