What's at stake, said Marvin Ammori, counsel to advocacy group Free Press, is no less than "the future of online television and the future of the Internet," He said that Comcast's decision to target peer-to-peer traffic has the effect of "disrupting investment and innovation" in other online video companies, which compete with Comcast.

But Comcast Executive Vice President David Cohen said the company is only trying to make sure as many people as possible can access the Web on its network. "There's nothing wrong with network management," Cohen said. "Every broadband network is managed, and every network must be managed or no network would function."

He also said the slowing of traffic to peer-to-peer sites presents only a "virtually imperceptible effect on a very small number of users."

The FCC convened the hearing in response to complaints against Comcast filed last year by online video company Vuze and a coalition of net neutrality advocates after tests by The Associated Press revealed that the cable company was impeding traffic to peer-to-peer sites. The hearing drew several hundred people to Harvard Law School, where police had to turn would-be audience members away.

Comcast argues that it slows traffic, but only as a reasonable network management tool. The FCC in 2005 issued a policy statement endorsing net neutrality in principle, but also containing an exception for reasonable network management practices.

Some of the commissioners appeared to be concerned by the prospect that Internet service providers could effectively shut down other online businesses, as well as prevent their subscribers from accessing the Web, by degrading traffic.

"We must preserve the open and neutral character of the Internet," said Commissioner Jonathan Adelstein. "It is clear consumers don't want the Internet to be another version of old media dominated by a number of giants."

But the most definitive statements from the commissioners were about disclosure practices, with FCC Chair Kevin Martin saying that companies need to tell consumers about their policies.

"It seems important that, for any of these practices to be reasonable, they be conducted in an open and transparent way," Martin said.

Commissioner Martin Copps also criticized companies for their "black box" policies. "There an old Washington adage that decisions made without you are usually decisions made against you," he said.

For net neutrality advocates, disclosure is only one area where Internet service providers like Comcast need to make changes. The advocates are asking the FCC to declare that Internet service providers should not prevent consumers from accessing particular applications.

Timothy Wu, a Columbia Law School professor who coined the term "net neutrality," said that Internet service providers should not discriminate against lawful applications. "Whatever we think reasonable network management is, it should not include blocking lawful applications," he said.

FCC Chair Martin and Comcast's Cohen also got into a discussion about whether the agency had the authority to order Comcast to stop slowing traffic to peer-to-peer networks. In its written reply to the complaint, Comcast argued that the FCC did not have that power.

Martin asked whether that was the company's position. "If we order you to stop blocking ... do you think we have the authority to do that?" Martin asked.

"I'm not 100% sure," Cohen answered. "I'll get back to you."

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