The problem is that residential cable networks -- originally designed for TV signals -- are asymmetric, i.e., they offer much higher bandwidth on the downstream side than the upstream. Bandwidth-thirsty P2P protocols like BitTorrent, which automatically seeks out and uses available connections on the network, need as much or even more capacity in the upload direction. That means a small number of BitTorrent file-sharing sessions can soak up network capacity "like a glutton at an all-you-can-eat buffet who insists on planting himself at the trough," as networking expert Richard Bennett put it in a recent op-ed piece (defending Comcast's practices) on the U.K. tech Web site The Register.
Jim Martin, a professor at Clemson University who has written widely on BitTorrent and the Internet, estimates that just 15 BitTorrent sessions can significantly slow down Web browsing for other users on the network.
"In areas and at times of congestion, which is only created by the P2P services, we manage the upstream part of that traffic," said Fitzmaurice, arguing that such management is entirely legitimate.
BitTorrent CEO Ashwin Navin, for one, does not view this as a competitive struggle: "I'm very sympathetic to the predicament they find themselves in," he said. "Most ISPs sold more capacity than they actually have. In next 12-18 months, with the explosion in BitTorrent-enabled applications that are all going to be using that capacity, they're going to have to really start to invest in their network."
Indeed, Comcast is taking two steps to deal with the predicament: it's planning a major network upgrade, to take effect late this year, that will provide nearly symmetric connections in the 100 Mbit/s range, and it's offering its own video download service.
At CES earlier this month, Comcast CEO Brian Roberts announced the launch of Fancast, Comcast's own high-speed download service for TV episodes and other content (but not full-length movies) over the Internet.
It's not just consumers who will be affected by the outcome of the service providers vs. the P2P-guys battle: enterprises will increasingly rely on high-bandwidth file-sharing, P2P services, and other non-traditional forms of content distribution in coming years, according to Navin. BitTorrent has upgraded its protocols with such customers in mind.
"The BitTorrent client we've deployed commercially is very different than the open-source BitTorrent clients of the past," said Navin. "Enterprise CIOs can take comfort in the fact that we're now aware of other applications, we're polite to them, and we also poke fewer holes in firewalls -- we efficiently take advantage of the capacity existing in local-area networks for content distribution."