The FCC is investigating complaints that Comcast has interfered with peer-to-peer (P-to-P) traffic associated with file-sharing sites, in one of the latest developments in the crucial net neutrality debate.

As the topic hots up, advocated on both sides of the debate appeared at an FCC hearing at Harvard Law School on the subject, including a congressman who’s recently introduced a pro-neutrality bill.

Net neutrality requires that network providers not discriminate against websites or various types of traffic, and Comcast has come under criticism for its treatment of P-to-P traffic.

The company has publicly defended its practices. "Comcast does not block any website, application or protocol, including P-to-P. Period," said executive vice president David Cohen at the recent hearing.

The company only "manages" protocols such as P-to-P during limited periods of heavy traffic, he claimed, adding it did so in limited geographic areas, only managed uploads, not downloads, and merely delayed, rather than blocked, requests for uploads.

"It's true that to maximise our customer's internet experience, we do manage our network,” he continued. "But don't let the rhetoric scare you. There's nothing wrong with it. Our customers want us to manage network congestion so they can do what they want, when they want, at reasonable speeds."

However, others at Harvard remained critical.

Marvin Ammori, chief counsel for Free Press, an advocacy group backing net neutrality, said the FCC hearing was not about technical details. "It’s about the future of online TV and the Internet," he said. "By targeting P-to-P, Comcast is disrupting investment and innovation in its online competition."

Gilles BianRosa, CEO of Vuze, a video service that uses P-to-P technology, said that while his company competes with Comcast in the delivery of content, the latter holds an unfair advantage. "What we have here is a horse race, and Comcast owns the racetrack, " he said. "I agree the market should decide which services win ... but there is no market without basic ground rules and transparency. We believe corporate assurances of good faith are not enough."

In the jam-packed Harvard session, FCC commissioners also underlined how crucial the net-neutrality debate is to the future of the internet.

"Network operators are making choices right now that will determine how Americans communicate, now and in the future," said commissioner Michael Copps. "I am not saying that any or all of these practices are unlawful. I am saying that choices like these, when you add them all together, are going to determine what kind of internet we have in the future."

Another commissioner, Jonathan Adelstein, insisted the internet’s open and neutral character must be preserved. "Respect for the free flow of information was bred into our country from its founding," he said. "It is clear consumers don't want the Internet to be a another version of old media dominated by a number of giants."

Democratic congressman Edward Markey, co-sponsor of a pro-neutrality bill also spoke up. "The Internet is as much mine and yours as it is AT&T's and Comcast's," he told the crowd.

Much of the Comcast case has focused on bandwidth-hungry, file-sharing application BitTorrent.

However BitTorrent CTO Eric Klinker said it was wrong for the industry to view his company as a force "endlessly consuming bandwidth."

In fact, he argued, BitTorrent has actually solved a problem – of effectively moving large files across the internet. He listed a series of public and private-sector organisations, ranging from film studios to NASA, that employ P-to-P file sharing to deliver large files.

David Clark, a senior research scientist at MIT, predicted the whole debate could ultimately be settled by moving away from current pricing plans – which see network provider charge varying rates for a broadband line's speed, but not for the amount of content downloaded – to a cost schedule based more on data volume.