Comcast, the largest cable operator in the United States, on Thursday filed suit against the U.S. Federal Communications Commission challenging its ruling that Comcast illegally blocked video traffic on its network.

Comcast challenged the FCC finding made a month ago on the grounds that the FCC action “was legally inappropriate and its findings were not justified by the record.” (see TechSpin: Parsing the FCC's Comcast Decision)

Video file-sharing companies such as BitTorrent and Vuze have long charged that Comcast deliberately blocks or interferes with peer-to-peer video traffic between their companies and customers, which affects the viability of their businesses.

In response, Comcast said that it manages traffic on its network so that users don’t experience service degradation. The carrier said it does not specifically target any company’s traffic, but it must apply some “limited management of P2P protocols.”

But the video companies say that anything that slows down their traffic can be just as damaging to their businesses as outright blocking. (see Startups Battle Comcast Over Video Blocking)

Part of the problem is that carriers such as Comcast have their own Internet video libraries, so it is tough for them to duck charges of anti-competitive behavior.

The FCC decision and Comcast’s appeal harken back to the two-year-old, still-unresolved network neutrality debate that has raged in fits and starts on Capitol Hill and has left in its wake at least two failed bills and little clarity.