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Strange Bedfellows
Most agree that the recent spike in Internet traffic is due to video downloads and peer-to-peer file transfers, but nobody’s sure how much responsibility each one bears. ISPs know the traffic distributions for their own networks, but they’re not disclosing them, and a given ISP’s distribution may not reflect that of the Internet as a whole. Video downloads don’t hog bandwidth in the way that many peer-to-peer programs do, though. And we do know that peer-to-peer traffic is the type that Comcast clamped down on.

Nonetheless, ISPs and peer-to-peer networks are not natural antagonists. A BitTorrent download may use a lot of bandwidth, but it uses it much more efficiently than a traditional download does; that’s why it’s so fast. In principle, peer-to-peer protocols could help distribute server load across a network, eliminating bottle­necks. The problem, says Mung Chiang, an associate professor of electrical engineering at Princeton University (and a member of last year’s TR35), is the mutual ignorance that ISPs and peer-to-peer networks have maintained in the name of net neutrality.

ISPs don’t just rely on the TCP protocol to handle congestion. They actively manage their networks, identifying clogged links and routing traffic around them. At the same time, computers running BitTorrent are constantly searching for new peers that can upload data more rapidly and dropping peers whose transmissions have become sluggish. The problem, according to Chiang, is that peer-to-peer networks respond to congestion much faster than ISPs do. If a bunch of computers running peer-to-peer programs are sending traffic over the same link, they may all see their downloads slow down, so they’ll go looking for new peers. By the time the ISP decides to route around the congested link, the peer-to-peer traffic may have moved elsewhere: the ISP has effectively sealed off a wide-open pipe. Even worse, its new routing plan might end up sending traffic over links that have since become congested.

But, Chiang says, “suppose the network operator tells the content distributor something about its network: the route I’m using, the metric I’m using, the way I’m updating my routes. Or the other way around: the content distributor says something about the way it treats servers or selects peers.” Network efficiency improves.

An industry consortium called the P4P Working Group–led by Verizon and the New York peer-to-peer company Pando–is exploring just such a possibility. Verizon and Pando have tested a protocol called P4P, created by Haiyong Xie, a PhD student in computer science at Yale University. With P4P, both ISPs and peer-to-peer networks supply abstract information about their network layouts to a central computer, which blends the information to produce a new, hybridized network map. Peer-to-peer networks can use the map to avoid bottlenecks.

In the trial, the P4P system let Verizon customers using the Fios fiber-optic-cable service and the Pando peer-to-peer network download files three to seven times as quickly as they could have otherwise, says Laird Popkin, Pando’s chief technology officer. To some extent, that was because the protocol was better at finding peers that were part of Verizon’s network, as opposed to some remote network.

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