High-Def Dash

Switched digital video, it seems, has boiled down to serving a singular goal for cable operators: allowing them to add a slew of high-definition channels on the double.

Cable’s HD offerings were dramatically outpaced by DirecTV in 2007. The satellite operator was able to claim it offered as many as 85 high-definition TV channels to subscribers at the end of the year, with more on the way this year, compared with mid to high 20s for most cable providers.

In 2008, cable will try to sprint back to striking distance, in large part by swallowing big gulps of switched digital video.

Many cable operators “are really moving into high gear” on switched video deployments, said Greg Hardy, vice president of business development for Scientific Atlanta’s transmission network systems. “A lot of the ones we’re working with are trying to get as many HD channels out as they can, as quickly as they can.”

Time Warner Cable, for example, recently said it plans to spend about $50 million in North Carolina and South Carolina on a switched video rollout. The project, the operator claimed, will let it offer a virtually unlimited number of HD channels.

Time Warner declined to comment on whose switched video system it will use in the Carolinas. But it expects the deployment to be completed by mid-2008 but hasn’t disclosed how many new HD channels it will offer by then. Currently, Time Warner offers a maximum of 26 HD channels in the Carolinas.

The technology is appealing because it promises to at least double the amount of programming an operator can deliver, using the same amount of bandwidth. It may sound like hype, but switched digital video does — in theory — allows an operator to introduce an “unlimited” number of TV channels.

Unlike regular broadcast channels, a switched digital video system delivers a signal only when a set-top box requests it. Since, in a given neighborhood, at least half the channels in a typical lineup are probably not being watched, they don’t need to be transmitted to the houses in that area.

“As you get more experience with switched digital video, you find that some channels that are still in the broadcast tier are now suitable to be switched,” Hardy said.

When more programming is added to the switched tier, the chance that anyone will be tuning in to a particular show is even lower. That allows for greater “oversubscription” ratios: An operator can offer, say, 30 to 40 HD channels that may be less frequently watched, using bandwidth normally consumed by 10.

BigBand Networks chief architect for cable Doug Jones compares switched video to a huge Thanksgiving dinner. The people at the dinner table (i.e., viewers in a neighborhood) can’t possibly eat all the food (TV channels) that has been prepared — but it’s all waiting hot in the kitchen if anyone asks for a particular dish.

“A service group can only consume so much programming,” Jones said. “You’re going to see operators have the capability to carry a lot more HD simulcasts and even entirely new HD networks.”

The technology works because many of the 200-plus channels in a digital cable universe, including HD channels, are watched only occasionally. A Motorola viewership analysis of a typical cable system showed that two-thirds of the channels were viewed less than 10% of the day.

“The challenge is finding those channels,” Bruce Bradley, director of product management in Motorola’s Home and Networks Mobility business unit. “You can look at Nielsen [Media Research ratings], but there’s no metric for picking the least popular channels.”

Motorola has commitments from three large cable operators to deploy switched video in systems passing 24 million homes. (Comcast is among its switched video customers.)

When operators first started rolling out gear from BigBand, the switched video market’s earliest vendor, they tended to switch only standard-definition programming and opted to use the space that freed up to broadcast new HD channels. Some avoided switching HD signals, which typically require five times as much as bandwidth to deliver as SD, for fear of introducing technical problems.

But now, BigBand has seen several customers rapidly adding high-definition to their switched video groups. “We’re seeing systems that are well into the double digits with HD in the switched tier,” said Biren Sood, BigBand vice president and manager of cable video for the Americas.

Longer-term users of switched video also more actively consult BigBand’s traffic-analysis application, according to Sood. And, they use it to gather statistics not only for the switched tier but for the broadcast channels as well, constantly evaluating viewership patterns.

“A new channel may not be popular in the beginning of the year — making it a good candidate to be switched — but then becomes more popular a few months later,” Sood said.

BigBand switched video servers have been deployed commercially in systems representing more than 6 million homes passed by five operators, which include Time Warner Cable, Charter Communications, Cablevision Systems and Cox Communications. Sood said the vendor was scheduled to kick off commercial deployment with a sixth (unnamed) operator this month.

Still, while some operators are going full-throttle with HD and switched digital video, it remains a new technology for many local cable systems.

Bradley said Motorola is seeing a relatively conservative approach to switched video. There’s still concern that a switched video system be completely rock-solid, from set-top to headend.

“With broadcast TV, if someone’s set-top fails to tune to a channel, that affects your house,” Bradley said. “If a switched digital manager fails, you’ve taken out the ability of 50,000 tuners to get those switched channels. It’s the difference between blowing a fuse in your house and losing a power grid.”

Deployments, then, require careful engineering. Consider one effect of introducing switched video: The upstream traffic generated by set-top box channel-change requests can be significant when thousands of subscribers are surfing through switched programs at once.

“There are synchronizing events at the top of the hour and during advertising breaks when everybody’s flipping channels,” Bradley said.

Often, Motorola recommends that an operator upgrade portions of its plant to effectively handle all the upstream channel-change requests.

Big TV events actually reduce the load on the switched digital video infrastructure. Whereas a holiday like Mother’s Day puts a huge strain on phone networks, widely viewed television programs like the Super Bowl consolidate viewers on a single broadcast channel.

“When there’s a major sporting event you see subscribers leaving the switched tier and going to broadcast,” Bradley said. “With switched digital video, you have the most bandwidth usage when there’s nothing good on.”