Alliance Targets High-Speed Backplanes

Group aims to standardize multilevel signaling to boost the speed of backplane transceiver chips

November 28, 2003

2 Min Read
Alliance Targets High-Speed Backplanes

A coalition of chip and systems companies is launching an effort to standardize multilevel signaling, a doubling-up trick that can increase the throughput of backplanes.

The Multilevel Signaling Alliance was founded in July but is only beginning to make its presence known. A Web site for the group popped into existence Wednesday for a few hours before being replaced with an "under construction" screen ... as if someone had gotten to them ... (insert X-Files theme).

Representatives of Alliance members -- a list including Accelerant Networks Inc., Alcatel SA (NYSE: ALA; Paris: CGEP:PA), Force10 Networks Inc., and Sun Microsystems Inc. (Nasdaq: SUNW) -- couldn't be reached for comment Wednesday. Accelerant vice president of marketing Bill Hoppin returned a call but proved as elusive as the Cigarette Smoking Man.

"I can't comment on anything like that," he said. "If something were to transpire or come together, we'd definitely let you know."

It appears the Alliance's goal is to craft a standard that could then be adopted by one of the established standards bodies.

Multilevel signaling is a technique found in certain serializer/deserializer (SerDes) chips, such as those made by Accelerant. The idea is to send two bits per "symbol" -- that is, rather than send a zero or one for each clock pulse, the chip sends two bits: 00, 01, 10, or 11.

This doubles the number of bits sent without increasing the speed of the signal. The concept is important because at faster speeds, signals can't go as far without getting garbled.

Several vendors are investigating ways to increase backplane speeds, among them, Accelerant, Agere Systems Inc. (NYSE: AGR.A), Applied Micro Circuits Corp. (AMCC) (Nasdaq: AMCC), BitBlitz Communications Inc., Broadcom Corp. (Nasdaq: BRCM), Intel Corp. (Nasdaq: INTC), Marvell Technology Group Ltd. (Nasdaq: MRVL), PMC-Sierra Inc. (Nasdaq: PMCS), Rambus Inc. (Nasdaq: RMBS) (which doesn't make chips, but sells "cores" that go into other people's chips), Velio Communications Inc., and Vitesse Semiconductor Corp. (Nasdaq: VTSS).

Most have shunned a multilevel approach. Notable exceptions include Accelerant and Rambus, which have used PAM4 encoding to reach speeds up to 10 Gbit/s (see Accelerant Pulls Power Play and Rambus SerDes Hits 10-Gig).

Accelerant appears to be the only SerDes vendor involved with the Alliance. Rambus was invited but declined, says Jean-Marc Patenaude, Rambus's director of marketing.

Rambus isn't opposed to the idea of a standard. It's just that OEMs aren't crying out for one yet, Patenaude says. "So far, I haven't heard my customers say I need to work with Accelerant or Broadcom or Marvell," he says.

-- Craig Matsumoto, Senior Editor, Light Reading

For more about backplane transceivers, see our latest taxonomy project -- Who Makes What: Electronic Chips and Backplane Transceivers.

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