Defining HD Role for VOD


Time Warner Cable leads the cable industry with 120,000 HDTV subscribers, and given that it has deployed video-on-demand in nearly all its divisions, it has the industry's largest VOD reach.

Now, the company has finished lab trials that place HD content on VOD servers, with an eye toward launching that functionality in an unspecified near-term period.

Cablevision Systems Corp. last week beat Time Warner to the punch, though, launching HD on VOD. Yet when the No. 2 U.S. MSO enters this arena, the expectation is that its entire base of 4 million VOD set-top-enabled subscribers will have HD content available to it, making it the industry's largest HD on VOD deployment.

"We have gone through the processes and worked out the changes that need to be made in asset distribution and catchers to accommodate the transmission of HD," said Mike LaJoie, executive vice president of advanced technology. "The real effort is the HD file is so much larger. We didn't want to run into problems in transmission that would require re-sends."

Time Warner has been working with its satellite VOD transmission partners — In Demand and California Video Corp. — as well as N2 Broadband and its primary server vendors to iron out the integration issues related to HD content on VOD.

"We're talking about initially somewhere around 25 hours of HD at any one time on the server itself," LaJoie said. "The refresh rate depends on customer feedback and how much content is available."

HDTV content takes up to four times as much storage capacity as a piece of standard-definition programming. Hence, 25 high-definition hours would translate to perhaps 100 hours of SD content.

"We're pushing 1,800 and 1,900 hours changed out on a monthly basis now," LaJoie said, a far cry from the 200 hours Time Warner stored in 1999.

By next year, LaJoie said, the average capacity will near 2,500 hours, "so HD would be 4% of the space that's out there."

The evolution of storage technology also makes it easier to house HD content. Years ago, many of Time Warner's VOD launches used lots of branch servers located off the main servers, because storage was cheaper than transport.

"That equation has changed," LaJoie said. "Transport is much less expensive now."

MSOs can now centralize storage, so they don't need to store as many copies of VOD content in their systems. "The last several divisions we built last year were completely centralized. We pulled things back from the edge and moved to switched Ethernet and more aggressive optical transport like [dense wave-division multiplexing]."

In its Oceanic Cable system in Hawaii, for instance, the MSO has gone from 19 to four server locations. The storage is collapsed to the central hubs, LaJoie said, so the system's overall storage capacity remains the same — just spread over fewer sites.

"We're moving toward an implementation that's much more flexible for adding more storage, and we'll move away from storage tied to the video pumps," he said. "We're moving towards storage area network technology where you can add more streams if you need more streams."

As a side note, LaJoie said Time Warner's legacy server vendors are working on means to separate storage from streaming in existing deployments.

"Concurrent [Computer Corp.] uses fiber-channel arbitration loop technology. That lends itself to separation," he said. "SeaChange [International Inc.] and nCUBE [Corp.] have very well-tuned stripping technology across multiple disks," but both are working on stream and storage separation.

LaJoie said all of the legacy servers may not make the transition, but those that can't still could be used to house library product. "We'll still be able to use servers for their useful life. The payback on them is very short."

A second issue concerns bandwidth, but LaJoie doesn't foresee initial problems. Even at 120,000 homes nationwide, HDTV customers are a small subset of Time Warner's overall subscriber count, he noted.

"It does have an impact, but it just gets lost in the noise [for now]," he said.

"We can manufacture bandwidth in response to traffic," if penetration and contention rates rise, he added. "It's not so much splitting nodes, it's called optical segmentation."

One laser might feed an average of eight nodes, LaJoie explained. If HD grows in one area, optical service groups can be reduced to six or four nodes per laser.

"You can get down to a one-to-one relationship of laser to node, if need be," he said.

The biggest issue in HD VOD is "combining all the associated files into one file so you can transmit it as a single file," LaJoie said.

HD transmission files can get as large as 15 gigabytes, which presented a challenge because the original Unix software used to send files couldn't initially handle the various data batches that makeup an HD transmission, he said. But that has been rectified.

"HD is a very compelling format," LaJoie said. "And HD on VOD is something we can do and our competitors can't, and it's something we're interested in doing sooner rather than later."