July 11, 2007

Digital Video at Expo

Troubleshoots, Hockey Sticks and Open Loops

By Jonathan Tombes

The technical papers at this year's Cable-Tec Expo presented yet more evidence of how complex the industry's digital video network has become, switched digital video (SDV) and OpenCable being two cases in point.

Let's put the emphasis network complexity. The operational goal of most any technology deployment, of course, is to simplify and enhance the consumer experience.

Apart from a boost in channel offerings, for instance, transparency is part of the deal with SDV. In his Expo paper, Time Warner Cable Austin's Director of Digital Systems Todd Bowen explains, with a touch of irony, that "a strange thing" happened after activating the first node in July 2004, namely: "nothing."

Thereafter, he notes, a few trucks rolled, but those subsided. "This says a lot about the technology. It was totally transparent to the average subscriber," he writes.

Not that all SDV deployments have been as successful as that in Austin or that simplicity reigns in any case on the network side. For the benefit of those following the Time Warner Austin lead here, the large balance of Bowen's paper involves the sometimes tricky and nuanced "lessons learned" during this early rollout. (See this article in the current issue of CT for a summary of those lessons.)

Exponential curve

Another Expo paper (also from Time Warner Cable) highlights how SDV, by virtue of sheer mathematics, is poised to complicate life for the industry's digital video network engineers. Emanating from TWC's Advanced Technology Group, this paper by Senior Director, Video Systems, Glen Hardin and Senior Engineering Product Manager Tom Gonder offers up a troublesome hockey stick.

That stick is the exponential growth of narrowcast services. Starting from 78 cumulative streams in a legacy analog world, Hardin and Gonder note that over the past 15 years a medium size (TWC) market will have seen the addition of digital, ad zones, VOD, StartOver and now SDV. The corresponding cumulative rise in stream counts is from 78 to 378 when converting to digital, up to 650 by adding ad zones, next up to 7,450 by adding VOD, to 27,770 by adding StartOver, and finally up to 80,170 by adding SDV.
 
That's presumably a good thing for consumers. But what happens when the ads get played in the wrong zone, or VOD or switched program multicasts up with the wrong subscriber? Or more to the point, how do you keep that from happening? "The 'wall of monitors' is no longer an adequate means to monitor the system," they write.

Borrowing from the language of control theory, Hardin and Gonder posit the notion of "closing loops." Systems without a "feedback loop," they write, "tend to operate in an unpredictable or non-measurable manner." For more stability and accountability, they propose watermarks, or content identifiers, that can operate on both control and video planes.

OpenCable's open loops

The OpenCable initiative, kicked back into center stage by the FCC's deadline on removable security, follows the same pattern of a technology that aims at consumer ease, yet impacts the network in multiple and sometimes contradictory ways.

Here's a striking example. CableCards (the removable security portion of OpenCable) and SDV naturally both aim to benefit the subscriber, but as far as unidirectional host devices are concerned, the two are incompatible.

"Any channel that is put into SDV is unavailable to CableCard equipped (unidirectional) TVs and PVRs such as the TiVo Series 3," writes Bowen. The resultant subscriber experience of loss can be "emotional," he adds. (An understatement, given the psychological profile of a typical TiVo devotee.)

The CableCard itself has been known to do odd things, such as not authorize. What could the problem be? (See this article from last November's CT for TWC Data Support Services Manager Joanne Bandlow's answer to that and other CableCard FAQs.)

In terms of a systems technology, OpenCable has spawned a new breed of components designed to speak across vendor lines and, consequently, drive costs down and accelerate the development of features. Nonetheless, tradeoffs prevail, as usual.

"The benefits of interoperability come with an additional cost of system complexity," writes Sherisse Hawkins, senior director of set-top box development at (you guessed it!) Time Warner Cable, in another Expo paper.

Hawkins recommends specific ways to validate and integrate an OpenCable-compliant system's ability to initialize customer premise equipment (CPE), update firmware and application software residing on CPE, allow security and authorization (via the CableCard) and work with OpenCable host devices.

Also included in this useful Expo paper is a description of symptoms, probable root causes, and diagnoses for problems involving booting and initialization, applications, bidirectional communication and CableCards.

- Jonathan Tombes