The Renewable Bandwidth Balm
by Leslie Ellis // October 09 2006
Seems like every time you turn around, someone is proclaiming the life or death of the cable industry, as measured by its bandwidth. Usually, proclamations of the latter category sit in or near a sentence containing the words “Verizon” or “FiOS.”
Heres the short version of the “cable dies” tale: The “F” in cable’s “HFC” — hybrid fiber coax, its architecture of choice — doesn’t go far enough. Verizon’s fiber goes all the way home. If Verizon has deeper fiber, they must have better bandwidth. Therefore, cable will die.
Sorry. Too easy.
It’s true that there is no infinite vat of bandwidth, into which cable operators can dip out ladle after ladle of Gigabits. It’s also true that an HFC network carries a clever little feature, variously called “renewable” and “re-usable” bandwidth.
If you spend much time around the bandwidth saga, you tend to hear about “the tools in the toolkit.” It’s a list of six or so things that can be done to cable plant, without a lot of hassle, to preserve bandwidth: Split nodes. Go to 860 MHz. Use a switch.
“Use a switch” conversations usually beeline to the digital video portion of the network — video on demand, specifically. VOD is innately a switched service. When you order a show, it goes to you, and not necessarily to everyone on your system. Likewise, by not sending all channels to all customers, and instead switching channels onto the pipe only when requested, bandwidth is renewed. (See the March 27 and April 10 translations for more on switched digital broadcast.)
Byte and Switch
Yet what really got me thinking about this was a recent conversation I had with a Wall Street analyst, who asked the question a different way. He wanted to know how it is that cable operators can dedicate only one digital channel to the broadband connections of what can be millions of customers. How can one digital channel, with a downstream carrying capacity of 38 Mbps, serve the masses?
It turns out that broadband services are switched, too. Inside the headend component of every cable broadband system — known in the jargon as the Cable Modem Termination System, or CMTS — is a switching function. When stuff is coming in to you, it gets sent down the pipes that lead to you. It doesn’t go to everyone.
Heres how it works: Each CMTS consists of a series of “blades.” Blades are electronic boards about the size of a medium pizza box. They slide into an equipment cabinet.
(Should you see row upon row of these equipment racks, while suddenly noticing that you are freezing, you are probably in a headend.)
In the customer-facing direction, each CMTS blade contains ports (generally two for the downstream, six for the upstream), each of which connects to a strand of fiber. Each fiber goes to a neighborhood node. Each node can reach around 500 homes with services.
So, it isn’t really one channel feeding all broadband customers. It’s one channel times as many pockets of 500 homes served by that operator, or, one channel per CMTS port. That one channel dedicated to broadband Internet services gets re-used, hundreds of times, which renews the available bandwidth.
It’s probably worth noting that all voice over IP (VOIP) traffic runs on the same single channel used to shuttle broadband Internet services. Or, as one MSO observes: If the cable industry made as much money on all digital channels as it does on that one channel set aside for broadband and voice services, they could buy Verizon.
There’s a saying amongst cable old timers about capacity. It goes like this: Spectrum is what you’re born with; bandwidth is what you make of it. Switching is a way to make more bandwidth for the two big growth areas in cable — just about anything over IP, and video on demand.
That means there’s room for more growth spurts. The trick is figuring out what they’ll be, not who (cable or Verizon) has better bandwidth.
Ultimately, it comes down to this: When a resource is renewable, does it really matter who has more of it?
This column originally appeared in the Technology section of Multichannel News.