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Rival display interfaces face off in digital home

Posted: 01 Jul 2006 ?? ?Print Version ?Bookmark and Share

Keywords:DisplayPort? Unified Display Interface? UDI? display interfaces? HDMI?

Video has hit an impasse on the road to the digital home. Separate groups of engineers are finishing work on two incompatible display interfaces!DisplayPort and the Unified Display Interface (UDI)!vying to become the standard for a secure digital link in consumer systems and computers. The pair will compete against two digital interfaces already in use!Digital Visual Interface (DVI) and High-Definition Multimedia Interface (HDMI).

Thus far, no formal talks are scheduled among advocates of the new interfaces, and no one knows just how the competition will shake out. The confusion reflects unresolved conflicts among security, interoperability, ease of use and low cost at a time when the transition from analog to digital media is still in its formative stage.

"We've ended up with a nightmare scenario of multiple standards. It's a frightening mess," said Bob O'Donnell, VP of clients and displays at International Data Corp. "The notion of a converged display interface may just go away."

But "this is a transition period," said Michael Epstein, manager of technology and standards for Philips Intellectual Property and Standards, so "everything may not be neat and clean." Epstein is finishing a content protection approach for DisplayPort that has the latest security features content owners want, but it will not work with the scheme used in today's DVI and HDMI. "It's not clear whether there's an immediate need for interoperability," said Epstein, given that shipments of DVI and HDMI are still relatively low, and the transition to digital is still young.

UDI uses the same form of content protection found in DVI and HDMI. But it lacks features, such as longer encryption keys and proximity restrictions that content owners want to see in next-generation systems.

All sides agree on the need to shave costs and broaden interoperability. Thus they want a single, royalty-free technology that could replace LVDS inside notebooks, supplant VGA in computers and displays, and link to DTVs, STBs and other consumer gear. Content owners fear that those older, unsecured interfaces will put their movies and TV shows at risk of illegal copying, so digital security to plug this "analog hole" is a key motivation.

"Analog VGA has been the PC standard for 20 years, but now we are seeing some pressure for all content to be protected, and we can't do that on an analog interface," said Bob Myers, who co-chairs the DisplayPort effort and manages a display technology group at Hewlett-Packard Co. "At some point, we will have dates by which we need to support copy protection."

According to In-Stat Inc., DVI shipped in more than 60 million systems, mainly PCs and peripherals, last year, while HDMI went into fewer than 20 million systems, mainly DTVs and STBs. But the two are expected to hit parity this year as DVI, which dates back to 1998, peaks and HDMI!created in 2002!surges.

As early as 2003, a group of PC makers, including Dell and HP, were chafing at HDMI's technical limits and royalty structure. The charge is roughly 4 cents per system, plus a membership fee that typically runs $15,000 a year. They developed DisplayPort as a royalty-free option designed to leapfrog HDMI and DVI on several fronts.

DisplayPort taps the electrical layer of today's 2.5Gbps PCIe bus and rides its coattails to bandwidths of up to 10.8Gbps over four channels. It also delivers an improved copy-protection scheme. DisplayPort uses a 128bit encryption key along with AES, rather than the 40bit key used in the high-bandwidth digital content protection (HDCP) spec. It adds support for checking the proximity of the transmitter and receiver, a new technique to ensure users aren't fooling a system to send content out to distant, unauthorized users.

The copy-protection scheme will not hit a 1.0 draft until Q3 2006. Then it must go through approval processes at various content organizations, such as the Advanced Access Content System, which oversees content protection for next-generation DVDs.

DisplayPort not only aims to replace the aging VGA, which effectively tops out at today's 1,080p resolutions. It also wants to replace LVDS, which is being stretched to as many as 10 pairs of links between a system and display to handle the bandwidth needs inside today's notebook computers.

Backers including Analogix Semiconductor, ATI Technologies, Genesis Microchip and Nvidia are expected to produce silicon supporting DisplayPort before the end of the year. Samsung and Philips are also backing the technology, which was officially approved by the 100-plus-member Video Electronics Standards Association in a late-April vote.

The rub is DisplayPort's incompatibility with HDCP. "It is not meant to interoperate, and it doesn't," said Epstein of Philips. "Content providers want to see security improvements with every generation." OEMs could build products that support both the new and old copy protection schemes without much trouble, he added.

Leslie Chard, president of HDMI Licensing LLC disagreed, citing projections that by the end of 2006, as many as 300 million systems using HDCP may have shipped. "How are you going to ask people to use another connector?" Chard asked. "I have not heard a demand for more protection from the content owners, nor have I heard a demand for lower royalties from OEMs, and we have more than 70 HDMI adopters in mainland China."

Although the DisplayPort spec is royalty-free, its contract stipulates reasonable and nondiscriminatory licensing for any patents that apply it. "If you are a DisplayPort adopter, you don't know what your rate will be. Ours is fixed," Chard said, although the HDMI contract does include adjustments for inflation.

Building on HDMI
For its part, the UDI positions itself as a PC version of HDMI, promoted chiefly by Intel and Silicon Image, a chipmaker that earlier helped define both the DVI and HDMI specs. UDI seeks to maintain compatibility with HDCP so that new systems can link to existing DTVs and STBs. It is targeted squarely at PCs, leaving its compatible big brother!HDMI!to own the consumer space.

Like DisplayPort, UDI is positioned as both an external replacement for VGA and an internal replacement for LVDS. It too uses PCIe and is available royalty-free. UDI is currently in 0.8-version draft. It plans to follow HDMI's example of using three data channels and one clock channel. Data rates have not yet been set, but are currently estimated to range from symbol rates of about 5Gbps at the low end to more than 8Gbps at the high end.

Systems may need an adapter or a UDI-to-HDMI cable to make a physical link. Besides Intel and Silicon Image, UDI backers include Apple, LG Electronics, National Semiconductor, Nvidia and Samsung.

UDI has slightly more bandwidth than HDMI, but it does not support a few of that spec's more consumer-oriented features, including audio and component video. That could save PC makers a few cents.

- Rick Merritt
EE Times

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