Pushing VOD to the Edge

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To get a handle on their rapidly growing video-on-demand services, Comcast and other cable operators are looking to implement content-distribution network architectures.

As cable operators increase their VOD offerings, soon “you won't be able to fit the whole library at the edge” in a cost-effective way, said Jim Owens, Motorola product marketing manager for on-demand video.

Comcast's Project Infinity, for example, is aiming to vastly scale up the amount of video on demand to someday deliver 100,000 or more choices, at least five times what the operator currently offers.

A CDN approach provides centralized storage and management of all content, and pushes the most-demanded content to the “edge” (i.e., to a headend), where high-reliability servers can provide quick response times.

The tradeoff is the cost of bandwidth versus storage at the edge, said Tom Rosenstein, vice president of product marketing at Verivue, a VOD-systems startup whose backers include Arris and Comcast. “There's a tipping point where it makes more sense to store it at the edge,” he said.

After all, not every headend across the country needs its own copy of Mr. Ed episode No. 5 — or the thousands of other obscure tidbits at the end of the long tail.

However, Rosenstein added, the long-tail curve does not flatten out as quickly as people were projecting. With a 10,000-asset library, Verivue has found, about 50% of the content is still accessed several times a day. “The assumptions that the caching servers at the edge can be small aren't true,” he said.

As such, it's probably best to “overcompensate on the cache at the edge” when moving to a distributed VOD architecture, said Concurrent vice president and general manager of video solutions James Brickmeier.

The game now is to maximize the VOD-serving efficiency at the edge, said Neil Glazebrook, product manager in Cisco Systems' video content platforms business unit.

Cisco's Content Delivery System, which it obtained with the 2006 acquisition of Arroyo Video Solutions, can pre-provision content using an algorithm that yields a 90% hit rate at the edge, the company claims. “There are many dimensions to what you cache,” Glazebrook said.

VOD content-distribution systems must also have intelligence about time of day, said Motorola's Owens. For example, he said, music videos are popular in the afternoon when kids get home from school while weekend nights are big for movies on-demand.

In any case, it's a safe bet that VOD libraries will keep getting bigger and that server software and hardware will have to keep up. SeaChange International's recently released Axiom On-Demand 5.5 software, for one, now supports up to 150,000 assets per site, up from 20,000 previously.

“The new design goals have to be around millions of assets,” said SeaChange vice president of product marketing Alan Hoff.