The Fractal Net

You’re downloading a file, or calling up a Web page. Suddenly, the cyberworld goes into suspended animation.

Why can’t the Internet provide more consistent service? One reason is a lack of insight into the overall pattern of traffic on the Internet. Now, researchers at AT&T Laboratories have come up with some surprising answers to what’s going on.

If you look at a plot of traffic through a network point over a minute, the trace will fluctuate wildly from one fraction of a second to another-an expected result. Now look at a day broken up in units of 100 seconds. On a voice network, the curve flattens out; instantaneous variations cancel each other out. But on the Internet, the AT&T researchers found the pattern of traffic had the same “bursty” character over long time periods as over short ones.

Such “self-similarity”-described by a type of mathematics known as fractal geometry-occurs often in nature. A coastline, for instance, has the same jagged appearance on a large scale as on a small one. According to Robert Calderbank, vice president for information sciences at AT&T Labs, the Net’s self-similarity stems from the way people use it. Lengths of Internet sessions range over a span of 6 to 7 orders of magnitude. As a result, the flow of data on the Net resembles the mathematically complex phenomenon of turbulence.

This knowledge is allowing network engineers and service providers to rework the rules of thumb that they have used for 70 years in designing the telephone system, Calderbank says. Routers that incorporate the more sophisticated-and accurate-traffic algorithms should help data move through the Internet with fewer of those finger-drumming delays.