At the end of February, the Federal Communications Commission (FCC) held a public hearing at Harvard University, investigating claims that the cable giant Comcast had been stifling traffic sent over its network using the popular peer-to-peer file-sharing protocol BitTorrent. Comcast argued that it acted only during periods of severe network congestion, slowing bandwidth-hogging traffic sent by computers that probably didn’t have anyone sitting at them, anyway. But critics countered that Comcast had violated the Internet’s prevailing principle of “Net neutrality,” the idea that network operators should treat all the data packets that travel over their networks the same way.
So far, the FCC has been reluctant to adopt hard and fast rules mandating Net neutrality; at the same time, it has shown itself willing to punish clear violations of the principle. But however it rules in this case, there are some Internet experts who feel that Net neutrality is an idea that may have outlived its usefulness.
Mung Chiang, an assistant professor of electrical engineering at Princeton University and a member of last year’s TR35, says that in the name of Net neutrality, network operators and content distributors maintain a mutual ignorance that makes the Internet less efficient. Measures that one group takes to speed data transfers, he explains, may unintentionally impede measures taken by the other. In a peer-to-peer network, “the properties based on which peers are selected are influenced to a large degree by how the network does its traffic management,” Chiang says. But the peer selection process “will have impact in turn on the traffic management.” The result, he says, can be a feedback loop in which one counterproductive procedure spawns another.
Programs using BitTorrent, for instance, download files from a number of different peers at once. But if a particular peer isn’t sending data quickly enough, Chiang says, the others might drop it in favor of one that’s more reliable. Activity patterns among BitTorrent users can thus change very quickly. Network operators, too, try to maximize efficiency; if they notice a bandwidth bottleneck, they route around it. But according to Chiang, they operate on a much different timescale. A bottleneck caused by BitTorrent file transfers may have moved elsewhere by the time the network operator responds to it. Traffic could end up being rerouted around a vanished bottleneck and down a newly congested pipe.
A little information about the data they’re ferrying, Chiang argues, could help network operators manage congestion better. He points out, for example, that the BitTorrent transfers that tend to consume the most bandwidth are video files. But not all frames of video are created equal. Some contain information that will stay fairly constant throughout a scene. Other frames, however, describe minor modifications that occur over time, and these can occasionally be dropped without disrupting the viewing experience. Chiang and his colleagues have created some videos comparing the results of congestion management techniques that selectively drop some frames of video.
Treating data packets differently–prioritizing some over others–is a violation of the most austere version of Net neutrality. But the idea finds support in what may at first seem an unlikely place. Eric Klinker is chief technology officer at BitTorrent, the company founded by Bram Cohen, inventor of the BitTorrent protocol and another alumnus of the TR35. Klinker testified on behalf of his company at the FCC hearings at Harvard, but he agrees with Chiang that on occasion, impeding BitTorrent video transfers can be harmless. Someone watching a movie, for instance, places a higher priority on the next 10 minutes’ worth of data than on the last 10 minutes’. Packets containing the movie’s end credits could thus be tagged to indicate their low priority, and the network operator would know that they could be delayed during periods of congestion.