Getting the Boxes to Align
For some systems, set-tops are the last piece of the puzzle
by Todd Spangler -- Multichannel News, 7/27/2008 8:00:00 PM
The final roadblock to deploying switched digital video — a technology long heralded for its potential to deliver more TV channels in less bandwidth — has come down to the home front.
There are two issues. First, the software in digital set-top boxes must be updated so they can communicate with the switched video systems in the headend.
Second, operators want to be able to keep delivering programming to devices that use CableCards, such as TiVo digital video recorders.
Both of these factors have held up deployments for some cable systems, according to Bruce Bradley, Motorola's director of product marketing for switched digital video.
To address the first, Motorola a few months ago initiated a program to embed switched digital video messaging protocols into the firmware for its set-top boxes.
“We've done the development in house, instead of relying on the [electronic program guide] vendors to implement the [switched video] protocols,” Bradley said.
Previously, the assumption has been that the on-screen guide code should handle the switched video communication. However, Bradley said, some systems have multiple guides deployed, including GuideWorks' i-Guide, Cisco Systems' SARA and Aptiv Passport (now owned by Macrovision).
For systems trying to launch switched video, the difficulty comes in trying to sync up release schedules for the different guide developers. “We think that by enabling the one last element in the system, we can get the solution to market in a more timely fashion,” he said.
Biren Sood, BigBand Networks vice president and general manager of cable video, noted that the vendor — an early leader in the switched digital video market — works with multiple vendors' guides.
But he also confirmed the complexity involved for systems with disparate guides. “Some sites have challenges with different permutations of guides. That's holding some systems back,” said. “Certain guide environments still have work to do.”
As for supporting the likes of TiVo DVRs, CableLabs has now certified switched digital video tuning resolvers developed by Cisco and Motorola.
About the size of small set-top boxes, the Cisco STA1520 or Motorola MTR700 switched digital video tuning adapters handle communication to and from the headend for switched channels, communicating with a TiVo DVR via a USB connector.
The lack of a solution for customers with TiVos “has been a gating factor for sure,” Bradley said. “You, as a consumer, would not like to lose those channels.”
Not every cable system has held back on switched video.
In general, operators such as Time Warner Cable and Cablevision Systems have more aggressively deployed switched digital video, while Comcast and others are still in trial deployments.
Greg Hardy, vice president of business development Cisco's Service Provider Video Technology Group, said sites that have been running switched video for a while are widening their use of the technology.
The rule of thumb for initial switched digital video deployments has been to use an “oversubscription” ratio of 2:1 — that is, to double the number of channels you'd normally broadcast over a group of quadrature amplitude modulators. The idea is to minimize the chance that all QAMs will be in use.
Now, some Cisco customers have upped that to oversubscription rates of 3:1. Hardy said one system (he wouldn't name) is delivering 54 HD and 54 standard-def channels in eight QAMs — normally only enough space for no more than about 20 HD MPEG-2 signals.
“When you talk about how to get to 100 HD [channels] to match satellite, you have to go to switched digital video,” Hardy said.
How aggressive individual MSOs are on switched video depends on their other priorities, said Gil Katz, Harmonic director of cable solutions and strategies. He pointed out that Comcast is looking strategically at eliminating analog channels in about 20% of its systems this year as a way to unlock spectrum.
“There's only a question of how much [switched video] will be done in 2008, and how much will be done in later years,” Katz said. “The nice thing about it is, it's not just a tool for freeing up more bandwidth — it's good tool for adding more programming.”
Comcast distinguished engineer Phil Gabler provided some insight into the MSO's technical trials to date, in a presentation last month at the Society of Cable Telecommunications Engineers' Cable-Tec Expo.
Comcast is currently testing Motorola and Cisco switched video platforms, and hopes to start working soon with BigBand, according to Gabler. The MSO hasn't said where those trials are happening, but three have been reported to be Cherry Hill, N.J., Denver and Minneapolis/St. Paul.
In terms of channel selection, Comcast is “focusing on a selection of 80 long-tail channels,” which are very rarely viewed. The MSO has allocated four QAMs for those 80 channels, an oversubscription ratio of 2:1.
The peak load on the switched video systems happens on Sunday nights. Comcast is putting some HD channels in the system, but has seen more “blocking” events — in which all the QAMs allocated for switched video are used to capacity — with HD since high-def signals take up much more bandwidth than SD.
Gabler also provided some hints into future projects. For example, he said, “We are starting to think about [Internet protocol] TV using switched video over DOCSIS.”
Ultimately, industry executives predict switched digital video will be widely deployed, by operators large and small alike.
“There's always a thirst for more bandwidth and more content,” said Richard Blenkinsop, vice president of marketing and business development for Vecima Networks.
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