U.S. cable broadband providers Comcast and Cox Communications are slowing BitTorrent traffic at all times of the day, not just during peak traffic, according to a new study by a German computer research group.

Comcast has insisted that it uses network management techniques to slow some peer-to-peer traffic during times of peak congestion, but the study from the Max Planck Institute for Software Systems suggests that Comcast and Cox are slowing BitTorrent traffic "independent of the time of day."

The study, using more than 8,000 nodes worldwide to test for BitTorrent blocking, found that Comcast was interrupting at least 30 percent of BitTorrent upload attempts around the clock. At noon, Comcast was interfering with more than 80 percent of BitTorrent traffic, but it was also slowing more than 60 percent of BitTorrent traffic at other times, including midnight, 3 a.m. and 8 p.m. Eastern Time in the U.S., the time zone where Comcast is based, according to tests run by users of the institute's Glasnost network testing tool.

Cox was interfering with 100 percent of the BitTorrent traffic at 1 a.m., 4 a.m. and 5 a.m., also Eastern Time, according to the tests.

Comcast downplayed the results. P-to-p traffic makes up 50 percent to 90 percent of a network's traffic, and BitTorrent users can be on the network at any time, said Comcast spokeswoman Sena Fitzmaurice. That means network congestion from BitTorrent doesn't just happen in the middle of the day, she added.

"P-to-p traffic doesn't necessarily follow normal traffic flows," Fitzmaurice said.

The Internet users who participated in the study may not be representative of Internet users overall, she added. The users who run the Glasnost tests may be "heavy users of p-to-p," Fitzmaurice said.

Cox did not have an immediate comment on the study.

Comcast issued a statement repeating its earlier position that it "does not, has not, and will not block any Web sites or online applications," including BitTorrent.

"We have acknowledged that we manage peer-to-peer traffic in a limited manner to minimize network congestion," Comcast's statement continued. "While we believe our current network management approach was a reasonable choice, we are now working with a variety of companies including BitTorrent [to] move to a protocol-agnostic network management technique."

Comcast announced in March that it would work with the company named BitTorrent to come up with new network management techniques.

The Max Planck Institute's study seems to confirm testimony by U.S. Federal Communications Commission Chairman Kevin Martin, who told U.S. lawmakers in April that Comcast's interference with BitTorrent traffic appeared to be widespread.