AT&T Inc. is building an Internet protocol-based video network that proponents believe will deliver, in effect, an infinite number of channels to subscribers (See “The IPTV Difference,’’ page 31.)
But if capacity is going to be the name of the game, the cable-television industry already has fiber networks in place that have been built with the ability to expand as needed. The result: More channels and services, when subscribers want them. And no need to dump the TV sets or, in some cases, the set-top boxes they already have.
“The very nature of the hybrid fiber-coaxial cable plant makes it very extensible. When you look at those things combined, we will be the winning platform, hands down,” said Cox Communications Inc. chief technology officer Chris Bowick.
According to Bowick, that combination of technical advantages includes:
- Digital transmission, or simulcasts, of programming to neighborhood distribution points.
- Switched broadcast video, where an operator only sends out a signal, when someone wants it.
- Node-splitting, which can double channel capacity by activating another fiber strand going into a node.
- Advanced compression, which squeezes more programs into a given amount of bandwidth; and,
- Channel bonding, where more than one channel can be glued together to provide high-definition programming or superswift loading of Internet content.
“The important point is our networks are poised with future extensibility,” Bowick said.
For instance, operators have begun to convert the delivery of analog and digital signals to all-digital, starting with digital simulcast, Bowick said, which is freeing up bandwidth.
In the typical 750-Megahertz cable plant, one analog signal uses an entire 6 MHz transmission “slot,’’ while eight to 10 digital signals can fit into the same space.
With digital simulcast, all signals are delivered in the digital format from the headend to the pedestal or “node” in a neighborhood. That saves bandwidth on the way to the node.
At the node, the signals are converted back to analog waves, so TV sets without a set-top box can tune to ESPN, Cable News Network or their local ABC affiliate.
“Digital simulcast provides us with a competitive advantage going forward,” Bowick said, because consumers can still use their current television sets.
Cable operators also are doubling the amount of data sent on a given video signal into the home. That saves bandwidth after the node, and effectively doubles the number of channels that can be broadcast into a home.
Operators also are looking at switching video signals in headend or hub locations, Bowick said, further freeing up bandwidth in the network for more channels.
If the American consumer wants access to an unlimited number of “channels,” which telcos say they can deliver on a switched basis, Bowick said cable operators will be able to match that service using switched technology.
Instead of broadcasting 200 channels from the headend to the home, the cable operator would broadcast only 120 channels to all subscribers. The other 80 channels could be used to deliver any one of hundreds or even thousands of channels, since the channel will get used only when a subscriber actually requests it.
Cable is banking on the next generation of data transmission techniques to deliver data at speeds up to 80 Megabits per second, said Ralph Brown, chief technology officer at industry research consortium CableLabs. This is possible with the third iteration of the Data Over Cable Service Interface Specification, DOCSIS 3.0, which CableLabs has developed.
Today, Bowick said, Cox is delivering 12 Megabits per second to homes in some markets, including Northern Virginia. “And we can go beyond that on the existing platform,” he said.
By comparison, AT&T plans to deliver 24 Megabits per second to the home, which would be shared between standard and high-definition TV, Internet access and voice services.
The new CableLabs specifications would “bond” two 6 MHz channels together. Cable operators use one 6-MHz channel, capable of delivering about 40 Mbps, to deliver high-speed data service to the home. Bonding two channels together would double the speed. There is no theoretical limit, so operators could bond four channels together, offering 160 Mbps into neighborhoods, Brown said.
Cable nodes are the last piece of physical hardware that video, voice and data services travel through before reaching the home. Most nodes serve about 500 households.
At 60% video penetration, that’s 300 homes each getting 16 Mbps of capacity at the same time.
Operators can split those nodes further, into 250 home increments, effectively doubling capacity again, Brown said. Instead of 300 homes getting 16 Mbps, 300 homes could get 32 million bits per second. “You just light up another fiber and connect the downstream coax at the node,” he said. “It’s a relatively straightforward process.”
“Most [operators] put plenty of dark fiber in their networks when they deployed it at the beginning,” Bowick said. To split a node requires some modulation upgrades, he said, “but that is an inexpensive thing.”
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