Casting doubt on previous assertions from cable giant Comcast about its traffic management policies, the Max Planck Institute today released a study showing that the U.S. company has engaged in routine blocking or throttling of BitTorrent files at all hours of the day -- not just in periods of "peak congestion" as the company has claimed.

The new study also shows that cable rival Cox Communications also delays BitTorrent file-sharing activity, which has been estimated to consume a large percentage of traffic across the Internet.

Based in Philadelphia, Comcast is the nation's No. 2 Internet service provider, with 14 million subscribers. With 3.8 million, Atlanta-based Cox is the fourth largest provider in the U.S.

The Comcast-BitTorrent dispute has become a flash point in the ongoing debate over "net neutrality" and the obligation of Internet providers to offer consistent and transparent levels of service to all users, regardless of protocols, applications, or bandwidth levels.

In March, after reports in the press of Comcast's traffic-management practices caused a public outcry and moved the FCC to launch a series of hearings on the matter, Comcast said it would cease interfering with file transfers using the BitTorrent protocol by the end of this year. BitTorrent and Comcast reached an agreement to launch a "collaborative effort" involving "the broader Internet and ISP community" to seek a solution to the bandwidth-thirsty file-sharing protocol running over Comcast networks. Comcast said it will seek new bandwidth-allocation techniques later this year that will be "protocol agnostic." In practice that means that Comcast will simply shift from slowing specific applications to limiting speeds to any users that consume high amounts bandwidth.

In the past, Comcast has said that it restricts its bandwidth-constriction practices to "responsible and limited management in those limited geographic areas and at those limited times when it is required" " i.e., at peak periods such as early evening, East Coast time. The Planck study, however, concluded that such BitTorrent applications are being limited at all times of the day -- not just at times of peak traffic.

Software engineer Robb Topolski, who first sparked the BitTorrent controversy when he noticed his connection being throttled last year, testified at an FCC hearing in Palo Alto, Calif. last month that such traffic-slowing was occurring in the wee hours: he tested for interference by Comcast at 1:45 a.m., for instance, and discovered delays.

A Comcast spokeswoman in Washington D.C., Sena Fitzmaurice, acknowledged in a phone interview that "P2P traffic is not diurnal." BitTorrent users tend to be active at odd hours, she added, "which is why that kind of traffic is so difficult to manage."

"Comcast does not, has not, and will not block any websites or online applications, including peer-to-peer services like BitTorrent," the company repeated in a statement released today. "We have acknowledged that we manage peer-to-peer traffic in a limited manner to minimize network congestion."

The Planck Institute study included more than 8,000 users from around the world using a "packet-sniffing" tool called Glasnost to test whether BitTorrent traffic is being manipulated or delayed. The map below shows hosts with file-transfers being jammed marked in red. The tests were carried out between March 18th and May 15th of this year.

This map shows the results of a study of BitTorrent traffic interference by Internet service providers by the Max Planck Institute for Software Systems in Saarbruecken, Germany. Locations with hosts that had BitTorrent transfers being blocked or throttled are marked in red.

Founded in 2004 and based in Saarbruecken, Germany, the Max Planck Institute conducts basic research on the design and analysis of complex software systems. It's one of dozens of institutes operated by the Max Planck Society, named for the German physicist who helped develop the quantum theory.