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DSG’s a Key to Open Systems

Cable-industry engineers have long pined to open up their “closed” Scientific-Atlanta Inc. and Motorola Inc. cable systems as a means to drive better feature sets and gain leverage in pricing negotiations.

While much of the world relies on a Digital Video Broadcast (DVB) open-standards architecture for TV signaling, U.S. cable MSOs have used closed systems from S-A and Motorola.


But the advent of Data Over Cable Service Interface Specification signaling-gateway technology (DSG) gives a cable operator the chance to use a different, Internet protocol-based upstream protocol for signaling from the set-top to the headend, via cable-modem termination system.

“DSG is a set of protocols to allow [a CMTS] or other edge devices to handle the communication protocols,” said Arris Group Inc. senior director of multimedia products Mike Caldwell.

Three CMTS products have now been qualified for DSG use, and it appears MSOs will begin testing the technology in set-tops later this year.

Arris, one of three vendors with DSG-approved CMTS gear, said it will test with an unnamed operator later in 2005. Time Warner Cable plans such a test, said senior vice president of subscriber technologies and advanced services Mike Hayashi.

“DSG makes things easy,” he said.

For the past several years, cable set-tops have included cable modems, but they’ve never been activated by cable operators, Caldwell said.

With the CMTS approvals, MSOs can now activate the DSG protocols, so that VOD ordering and trick-mode commands can travel from the set-top to the VOD service through the cable system’s IP backbone, via the CMTS.

“It offers a new alternative for signaling management from the set-top box,” Caldwell said. “All set-top communications are done via DOCSIS.”

It’s the first step towards the operator’s long term goal of getting all system traffic onto an IP platform, Caldwell said. Older set-tops had three basic parts — Caldwell said: a downstream tuner, a Moving Picture Experts Group decoder to handle digital-to-analog conversions and an upstream modulator.

“In a DSG-enabled set-top box, the upstream modulator is replaced and a downstream tuner has been added to listen to a DOCSIS channel,” he said. “That’s what people will be trialing. It’s the first step towards freedom from S-A and Motorola and moves management traffic into an IP world.”


But despite Sony Corp.’s work on its Passage technology and S-A’s progress with its overlay system, it’s not clear cable operators are in a position to open up their networks. Legacy linear channels still use proprietary encryption technologies from S-A and Motorola.

And there are actually fewer set-top providers today than there were several years ago, with Pioneer being the latest company to withdraw from the U.S. set-top environment.

Still, it’s an important step for MSOs, said Caldwell, as the industry wants to move to an all IP transport structure over time.

Activating the modem also means moving to IP video delivery is done in very small, incremental steps, like displaying Internet content on the TV screen. That’s something SBC Communications Inc. said it will offer to consumers this year.