PHILADELPHIA, PA — Comcast is under investigation by the Federal Communications Commission again. This time the set-to is over allegations that the biggest cable-and-internet operator in the U.S. is giving preferential traffic priority to its voice-over-internet-protocol telephone service at the expense of competitors’ similar services.Comcast on Friday responded to an FCC request for more information about the VoIP allegations with a chilly but polite letter saying, essentially, “bull.”

“[Comcast Digital Voice] is a service separate from Comcast’s [High Speed Internet] service; [CDV] does not run over Comcast’s HSI service,” Kathryn A. Zachem, vice president for the cable giant’s regulatory and state legislative affairs department, wrote in a letter to the FCC. “CDV, like Vonage or Skype, is an IP-enabled voice service (i.e., it uses Voice-over-Internet-Protocol to deliver the service). However, unlike Vonage, Skype, or several other VoIP services, CDV is not an application that is used ‘over-the-top’ of a high-speed Internet access service purchased by a consumer. Significantly, CDV customers do not need to subscribe to Comcast HSI service, and Comcast does not route those CDV customers’ traffic over the public Internet. Rather, as the Commission is aware, our CDV service is based on PacketCable™ specifications that ‘mandate the use of a managed IP network, in that services are not delivered over the Internet.’ Many companies offer IP-enabled services over their networks, including voice and video services that are distinct from their high-speed Internet access service.”

Zachem’s letter was in response to one sent by the FCC to Comcast on January 19th. In the FCC’s letter, the agency noted the VoIP questions were part of a follow-up to the FCC’s recent investigation of Comcast’s “bandwidth throttling” as a strategy for managing network congestion. The cable company discontinued that practice late last year after receiving a slap on the wrist from the FCC.

In the letter, Comcast maintains that its CDV service is less similar to Vonage and other VoIP providers’ services than it is to wireline telephone companies’ services. That opens a whole new can of worms for the cable company, though, as the FCC suggested in its January 19th letter that CDV might be subject “to the same intercarrier compensation obligations applicable to other facilities-based telecommunications carriers.”

Wary of finding itself mired in telco regulations, Comcast attempted to extricate itself from that web, as well. The cable company quoted from the FCC’s 2002 Cable Modem decision, which classified cable-based services as “information” rather than telecommunications.

“Although the transmission of information to and from… computers may constitute ‘telecommunications,’ that transmission is not necessarily a separate ‘telecommunications service,’” the controversial order, still in force, ruled.

There are a couple of issues with Comcast’s response. Most notably, the letter the cable company received was sent the day before former Chairman Kevin J. Martin’s tenure at the agency expired. Martin was a vocal supporter of the Cable Modem decision. His successor, interim Chairman Michael Copps, voted against the decision.

“Today we take a gigantic leap down the road of removing core communications services from the statutory frameworks established by Congress,” Copps warned after the 2002 vote. “… [We’re P]laying a game of regulatory musical chairs by moving technologies and services from one statutory definition to another.”

Observers have speculated that Comcast may be facing a tough challenge in convincing the FCC to back off its latest inquiry.