The decision by Echostar, which has more than 4 million customers, could make it harder for the consumer electronics-centric IEEE-1394 standard to become dominant. And if DVI, a high-speed digital baseband interface originally developed for PCs and their monitors, gains an early toehold, the industry will likely be stuck with it. "It's hard to eliminate something once it gets into the box," said Mark Kirstein, a director at Cahners In-Stat Group, though he added, "I'd be surprised if TV manufacturers embrace DVI."

Echostar "is already working on the incorporation of a DVI with High-Bandwidth Digital Content Protection HDCP in our next-generation box," said Dave Kummer, vice president of engineering at Echostar Technology Corp. (Littleton, Colo.), a technology arm of Echostar. Some TV manufacturers are also adding a DVI with HDCP in their TV sets, he added.

CableLabs, the R&D lab for U.S. cable operators, is also "investigating DVI and a few other digital interfaces, not as a competing interface but as complementary to IEEE 1394," said David Broberg, director of OpenCable requirements at CableLabs (Louisville, Colo.). The group has yet to determine whether there is sufficient added value in specifying DVI as an enhancement for the current generation of the OpenCable spec, but plans to conclude its evaluation "by the end of this year," said Broberg.

Nobody is arguing that IEEE 1394, a two-way high-speed interface capable of sending command and control protocols, will be replaced by DVI, essentially a point-to-point digital interface designed to send uncompressed streams. IEEE 1394 is inherently suited for recording and networking applications within the home, while DVI is pitched as an interface between a graphics chip and various kinds of monitors, including plasma display panels, LCDs and even CRTs.

Industry opinions sharply diverge, however, when the debate turns to whether 1394 should be the only digital interface in a set-top, or if DVI might be needed as a preferred point-to-point interface for digital TV.

"If you use DVI to connect your set-top to your digital TV, you will still have to have 1394 when you want to record from the set-top to your DVD or D-VHS," said Lee Ratliff, product manager at Texas Instruments Inc. Because1394 will be required in a set-top anyway, in Ratliff's view, "DVI is just an unnecessary cost."

Scott Fierstein, technical evangelist for consumer audiovisual platforms at Microsoft Corp., agreed. "DVI may become an optional check box for set-tops, but the IEEE 1394 will be a standard interface," he said. "DVI does not remove the need for IEEE 1394."

"Some cable operator customers are asking about DVI, but none have specifically required it," said Dan Ward, director of marketing for the Cable and Communications Division at Pioneer New Media Technologies Inc. (Burbank, Calif.). Asked if both 1394 and DVI may be required in a future set-top, Ward said, "It will more than likely be one or the other, but not both, unless we offer one as an add-on option."

When most digital content received at home from DVD, satellite or cable is based on MPEG-2 streams, "it makes sense to use 1394 as an interface to send the bits — kept in MPEG-2 — to and from a storage device," said Scott Smyers, vice president at Sony's Interconnect Architecture Lab, part of its U.S. research operation.

Simple as possible

In contrast, Echostar's Kummer believes using 1394 to connect set-top and TV is simply "not a good idea." He said, "We want to keep a digital interface as simple as possible so that there will be less chance of misinterpretation or causing interoperability problems between various set-tops and TV receivers in implementing the interface."

Kummer said it's no trivial task to design a set-top box capable of using 1394 to send state-of-the-art graphics to a TV — or even an advanced electronic program guide with, for example, a video window that can be collapsed into a corner of a display. Indeed, a major part of the debate over using DVI or 1394 revolves around their suitability for carrying high-quality graphics.

Similarly, it's far from easy to design a set-top with a hard-disk drive that can send the streams known as trick mode — such as fast-forward, rewind or slow — via 1394. "Doing such trick modes in the high-definition video streams is almost completely impossible," Kummer said.

This is because 1394 expects to send and receive content based on a fully compliant MPEG-2 transport stream. Sending, for example, a fast-backward stream over 1394 to a TV will probably require brute force, said Kummer. The easiest way is to get the baseband image from the set-top, find the I-frame, correct time stamps, create a fast-backward stream and encode it once again to an MPEG-2-compliant transport stream before shipping it off to a TV set, he said.

In some ways, the whole 1394 vs. DVI issue might be seen as a neverending debate over where the ultimate intelligence — decoding, graphics-rendering capabilities and so on — should reside: inside a set-top box or within a TV.

Three options

In-Stat's Kirstein laid out three options for consumer electronics companies in connecting a set-top to a DTV. The first is a 1394 connect with full interactivity, in which the "set-top can become a dumb network interface card." Option 2, Kirstein said, is to use a component analog connect, which provides "interactivity only through the set-top." In this scenario, "The set-top has all the value and the TV becomes a dumb terminal." Option 3, DVI, provides "no real interactivity," he said, and the "TV still becomes a dumb terminal."

Kirstein concluded that a very large part of the market will adopt 1394, since "DVI won't support expansion, storage, networking, cameras and so on, which will become increasingly important as CE consumer electronics devices move to digital."

According to Echostar's Kummer, the 1394 vs. DVI debate first kicked off when Hollywood studios vehemently opposed plans to send high-definition video streams "in the clear" in RGB or YPrPb format from a set-top box to a TV. The original agreement among consumer electronics manufacturers, to which Echostar also agreed, was to incorporate IEEE 1394 in a set-top as an interface with a storage medium. The proposed interface between the TV and the set-top was either RGB or YPrPb.

Responding to Hollywood's objections, 1394 proponents suggested embedding 1394 with an encryption-based link layer called the Digital Transmission Content Protection (DTCP). "That's when we stood up and said we don't think 1394 is the right interface for TV," Kummer remarked.

Subsequently, DVI added its own protection scheme, called HDCP, developed by Intel Corp. Microsoft's Fierstein observed that HDCP has Hollywood's blessings to the same extent as DTCP. But proponents of both DVI and 1394 observed that at this point, the debate over a set-top box-digital TV interface has little to do with the technology issue of copy protection schemes.

The technology fistfight between DVI and 1394 erupts at a point when the TV market is already in an uproar over the transition to digital. At a time when the FCC is ordering the cable set-top business to go retail with boxes based on the OpenCable specifications, service providers fear losing control of the interface. That's why they insist that it's important for subscribers to see the service providers' own unique GUI or electronic program guide displayed on screen rather than an interface created by a TV manufacturer.

But some observers, such as Sony's Smyers, believe they are destined "to lose that control." Consumers will go out and buy whatever set-tops they want. In some cases, the majority of set-top functionality may be incorporated inside a TV. "Poorly implemented low-end set-tops won't be able to show much of the fancy electronic program guides intended by operators," he said.

Complicated lives

On the viewer's side, throwing DVI into the mix of disparate interfaces can only complicate the lives of consumers, who would be forced to figure out what interface their set-tops and TVs are using. "I don't see how adding DVI could stabilize the market," said Smyers.

Though proponents maintain that using DVI in a set-top is much easier than adding a 1394 interface, others counter that adding DVI to a system that already has 1394 could be "a pain." It means creating multiple high-speed paths inside the set-top architecture, said David Fair, manager of the visual technologies initiative at Intel. The set-top must incorporate another frame buffer, the ability to decode the MPEG-2 stream, and the ability to select and send a DVI stream. It also requires additional cabling and a connector. "Most likely, that will not be a trivial cost," Fair said.