Last summer, the FCC ordered Comcast to stop blocking users' access to online content and services. Comcast was also required to fully disclose details of both old and new network -management practices.

An FCC letter to Comcast on Sunday asked the company to justify its treatment of similar services from competing providers. Comcast has until Jan. 30 to respond and said it is reviewing the letter.

"We seek clarification with respect to an apparent discrepancy between Comcast's filing and its actual advertised practice," wrote Kathryn Zachem, vice president of regulatory affairs for the FCC, and Matthew Berry, FCC general counsel.

The FCC's Concern

Zachem and Berry took exception with a Sept. 19 submission in which Comcast said that if a consumer uses 70 percent of his provisioned bandwidth for 15 minutes or more when his neighborhood Cable Modem Termination System (CMTS) node has been near capacity for a period of 15 minutes or more, that consumer loses priority when routing packets through congested portions of the network.

If a consumer them places a VoIP call along the congested route, Comcast said customers may find that VoIP calls "sound choppy." Comcast didn't distinguish between the performance of its service and competing services in its Sept. 19 submission. However, the FCC thinks Comcast's Web site suggests that a distinction exists.

The FCC pointed to a portion of Comcast's Web site that reads, "Comcast Digital Voice is a separate facilities-based IP phone service that is not affected by this [new network management] technique." Comcast's Web site adds, "VoIP providers that rely on delivering calls over the public Internet ... may experience a degradation of their call quality at times of network congestion."

The FCC's Demand

The FCC wants Comcast to explain why it omitted from its filings the effects that its network-management technique has on Comcast's VoIP offering versus competing products. The FCC also wants Comcast to offer a detailed justification of its treatment of its own VoIP service compared to competing offers on its network.

Finally, the FCC stressed the need for Comcast to explain how Comcast Digital Voice is "facilities-based," how it uses Comcast's broadband facilities, and whether -- and if so, how -- Comcast Digital Voice affects network congestion in a different manner than other VoIP services. As the FCC understands it, Comcast's VoIP service is not yet complying with intercarrier compensation obligations.

Ben Scott, policy director of Free Press, said the letter is a positive sign that the FCC's Comcast decision was not a final action on Net neutrality. Scott is pleased that the commission is conducting an ongoing investigation into network-management practices that might impact users' access to online content.

"An open Internet cannot tolerate arbitrary interference from Internet service providers. Congress and the FCC must close any legal loopholes that permit anticompetitive behavior to thrive," Scott said. "As the agency transitions into the new administration, this letter demonstrates that vigilance for consumer protection will not be put on hold."