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But the idea that an Internet service provider (ISP) would make value judgments about the packets traveling over its network makes many people uneasy. The Internet, as its name was meant to imply, is not a single network. It’s a network of networks, most of which the average user has never heard of. A packet traveling long distances often has to traverse several networks. Once ISPs get in the business of discriminating between packets, what’s to prevent them from giving their own customers’ packets priority, to the detriment of their competitors’? Suppose an ISP has partnered with–or owns–a Web service, such as a search engine or a social-networking site. Or suppose it offers a separate service–like phone or television–that competes with Internet services. If it can treat some packets better than others, it has the means to an unfair advantage over its own rivals, or its partners’, or its subsidiaries’.

The idea that the Internet should be fair–that it shouldn’t pick favorites among users, service providers, applications, and types of content–is generally known as net neutrality. And it’s a principle that has been much in the news lately, after its apparent violation by Comcast, the second-largest ISP in the United States.

Last summer, it became clear that Comcast was intentionally slowing down peer-to-peer traffic sent over its network by programs using the popular file-sharing protocol BitTorrent. The Federal Communications Commission agreed to investigate, in a set of hearings held at Harvard and Stanford Universities in early 2008.

It wasn’t BitTorrent Inc. that had complained to the FCC, but rather a company called Vuze, based in Palo Alto, CA, which uses the BitTorrent protocol–perfectly legally–to distribute high-­definition video over the Internet. As a video distributor, Vuze is in competition, however lopsided, with Comcast. By specifically degrading the performance of BitTorrent traffic, Vuze argued, Comcast was giving itself an unfair advantage over a smaller rival.

At the Harvard hearing, Comcast executive vice president David Cohen argued that his company had acted only during periods of severe congestion, and that it had interfered only with traffic being uploaded to its network by computers that weren’t simultaneously performing downloads. That was a good indication, Cohen said, that the computers were unattended. By slowing the uploads, he said, Comcast wasn’t hurting the absent users, and it was dramatically improving the performance of other applications running over the network.

Whatever Comcast’s motivations may have been, its run-in with Vuze graphically illustrates the conflict between congestion management and the principle of net neutrality. “An operator that is just managing the cost of its service by managing congestion may well have to throttle back heavy users,” says Bob Briscoe, chief researcher at BT’s Networks Research Centre in Ipswich, England. “An operator that wants to pick winners and chooses to say that this certain application is a loser may also throttle back the same applications. And it’s very difficult to tell the difference between the two.”

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