The FCC sent a letter to the US cable provider earlier this week asking the company to clarify its position on voice-over-IP (VoIP) traffic handling.
The letter refers to a September filing in which Comcast told the FCC that it did not distinguish between VoIP traffic generated by its own Digital Voice service, and VoIP calls from competing services.
However, the FCC cited a recent Comcast FAQ page, which warns that traffic on other VoIP services could be slowed at times of peak usage, reducing call clarity, while its own service would not see such degradations.
The company contends that its service uses a "facilities-based" system not subject to the caps. The FCC is seeking clarification on this system.
"We request that Comcast explain why it omitted from its filings with the Commission the distinct effects that Comcast's new network management technique has on Comcast's VoIP offering versus those of its competitors," reads the letter.
"To the extent that Comcast maintains that its VoIP offering is a telephone service offering transmission facilities for VoIP calls distinct from Comcast's broadband offering, then it would appear that the fee Comcast assesses its customers for VoIP service pays in part for the privileged transmission of information of the customer's choosing across Comcast's network."
The matter could be of particular concern to both sides as it comes just months after the settlement of a similar net neutrality dispute stemming from Comcast's handling of peer-to-peer service traffic.
Comcast settled the issue by agreeing to cap bandwith usage for all users, rather than specific types of network traffic.
If the company is indeed providing preferential access to its own VoIP service, the FCC warned that Comcast could be subject to further action.
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