Comcast Digital Voice and VoIP

I was surprised to hear this week that the FCC is going to probe Comcast's differential treatment of internet telephony services from their own Digital Voice service. The issue is supposedly, since both are VoIP, that if they treat them differently then they are discriminating. In particular, the VoIP-based services of others can be throttled like other internet traffic, yet Comcast's service is not. Therefore this becomes a question of network neutrality.

This is hogwash. The problem appears to be a confusion between technology and service. This may or may not be deliberate on the part of an FCC that has been, by many accounts, biased against the cable companies versus the telephone companies. Regardless of the political angle, let's look at the technology and understand better what is going on here.

First, VoIP is a technology not a service. Like every PacketCable-compliant operator, which covers pretty well every North American cable company, Comcast's own telephony service is based on VoIP technology. Without delving into technical details, this means that the voice and associated call-control signalling rides on the TCP/IP protocol stack, which itself rides on top of the digital coaxial cable service (or hybrid coax+fibre), which serves as Layer 1 (physical layer) of the protocol stack.

Like every other service on the coax, telephony service is allocated exclusive bandwidth (or a channel if you prefer). This channel is quite narrow in comparison to the coax capacity, which is typically at least 750 MHz these days, except that since the coax is common to many subscribers the total bandwidth consumed can be much higher. There are other channels set aside for digital television and broadband internet. The television channels are quite wide but the amount of bandwidth is independent of the number of subscribers. Broadband internet bandwidth, like telephony service, scales with the number of subscribers.

The fact that VoIP is used for the cable company's own telephony service is a red herring. They could use that bandwidth to support any other technology that is digital. The first generation of cable telephony was circuit-switched digital, not packet. And not all packet technology need be TCP/IP. But I suppose that since it wasn't VoIP technology it didn't trigger any zealotry.

In fact, the situation here is equivalent to the telephony and broadband segregation on the telephone company's DSL-enabled copper loops. Here each loop is dedicated to a subscriber, at least as far upstream as the DSLAM, with the analogue telephony and broadband internet services frequency multiplexed. Voice extends up to about 3 kHz, with the broadband data channel starting somewhat above that and continuing up to (depending on the technology) several MHz. Since the modems and telephones can misbehave when exposed to the other service's content, the DSL provider gets you put filters on each of your phones (the DSL modem has its filter built-in).

So all this FCC action is about inflaming latent resentment against the big bad company and not about actual bad behaviour. Like them or hate them, Comcast is doing nothing wrong. In this case it's the FCC at fault.

Maybe next they'll go after Verizon or another telco, wondering why plain old telephone service isn't subject to the throttling on DSL internet access services. The FCC would still be in the wrong, but at least then they'd be consistently wrong.