Comcast's traffic management practices have landed the cable giant in court. Yesterday, a California resident filed a lawsuit in state court accusing Comcast of breach of contract, breach of implied covenant of good faith and fair dealing, and violating the California Consumer Legal Remedies Act.

John Hart describes himself as a Comcast customer who has seen performance hits when using "Blocked Applications" targeted by Comcast's traffic management application, Sandvine. In his complaint, Hart says that Comcast severely limits "the speed of certain internet applications such as peer-to-peer file sharing and lotus notes [sic]." Comcast accomplishes this by "transmitting unauthorized hidden messages" to the PCs of those using the applications.

Hart also takes issue with some of Comcast's high-speed advertising. He upgraded his service to the Performance Plus package in order to get faster uploads and downloads, and also to use the "Blocked Applications" referenced in the lawsuit. Comcast, he says, did not adequately disclose its traffic management practices when he signed up for High Speed Internet or when he upgraded.

Some Comcast customers have suspected that the ISP blocks some P2P traffic, but it wasn't until last month that the company was caught in the act. Testing performed by the Associated Press showed conclusively that Comcast was using forged TCP reset packets to block BitTorrent traffic. It then emerged that Comcast's traffic management practices were causing problems for other applications, including groupware client Lotus Notes.

Comcast has steadfastly denied blocking traffic, but its explanations of what exactly it is that the company is doing have been unconvincing. The ISP says that it sometimes "delays" traffic, but that the "delayed" traffic will always eventually make it to its destination. A Comcast spokesperson told me today that, while the company does engage in network management like any other ISP, "we're not blocking anything." As was the case with Threat Level, he referred me to the company's FAQ for more information on what the company does and does not do with P2P traffic.

At the beginning of November, a few public interest groups filed a complaint with the Federal Communications Commission, accusing Comcast of running afoul of the FCC's Internet Policy Statement, and asking the Commission to prevent Comcast from engaging in any future traffic blocking. Hart's complaint also accuses Comcast of violating FCC policy by "impairing" the use of some applications while permitting other applications to operate without hindrance.

Hart is seeking class-action status for the lawsuit, damages, a change in the company's advertising to reflect its traffic-shaping practices, and an injunction barring Comcast from further interference with the "Blocked Applications."

A Comcast spokesperson told Ars that the company has not yet been served with the complaint, and therefore had no comment on the lawsuit.