Backplane Bandits Get Together
Next week, a group calling itself the High Speed Backplane Initiative (HSBI) is planning to launch.
The group's goal is to promote a common solution for the next hike in backplane speed, the primary conduit of bandwidth in many pieces of high-powered routing and switching gear. They see a need in the next year or so for backplanes that can support serial electrical signals at 5 Gbit/s -- twice the speed of today's state-of-the-art 2.5-Gbit/s backplanes.
The need is being driven by the fact that optical modules are getting smaller and line rates are going up, says John D'Ambrosia, secretary of HSBI and manager of semiconductor relations for Tyco Electronics. Systems vendors are talking about putting four or eight 10-gig modules on a line card, and at that density there are so many traces on the backplane that it becomes impossible to route them all.
A twofold increase in backplane speed might seem a little strange when the electronics of telecommunications interfaces are increasing by jumps of four (Sonet) or ten (Ethernet) times. But trying to achieve a fourfold hike in backplane speed didn't look technologically possible within the timeframe it was required, says Bill Woodruff, VP of marketing for Velio Communications Inc., another founder member of the HBSI.
In fact, work has only just begun on solving the technical problems of sending 5 Gbit/s over 30 inches of copper. "That's why we got together, 'cause we said, 'This ain't easy,' " Woodruff quips. There are a variety of ways of solving the technical issues, he says, and left to their own devices, components vendors would likely come up with an array of incompatible solutions.
Interoperability is vital, says Joel Goergen, chief scientist at Force10 Networks Inc., especially for a commodity part like a SerDes transceiver -- the chip that sends and receives the high-speed electrical signal over the backplane. Being able to chose compatible parts from a range of suppliers is essential if vendors like Force10 are to build next-generation systems cost-effectively.
There seems to be a broad consensus on that. The HSBI has nine founding members, mostly components vendors, including Tyco, Velio, Agilent Technologies Inc. (NYSE: A), Intel Corp. (Nasdaq: INTC), Gennum Corp. (Toronto: GND), Marvell Technology Group Ltd. (Nasdaq: MRVL), Mindspeed Technologies, Tality Corp., and Texas Instruments Inc. (NYSE: TXN). Systems vendors are represented among the 28 "supporter" companies that have been involved in discussions but have not signed a legal agreement.
The group has already made a couple of decisions. One of its early conclusions was to support multiple coding protocols over the backplane. These protocols decide how multiple 2.5-Gbit/s Sonet data streams are combined and split apart, or how a 10-gig data stream is broken up and recombined, so any size channel can be sent over a 5-Gbit/s link. In general, different schemes operate for Sonet- and Ethernet-based traffic.
"If some member voted for one scheme and some for another, then it's likely that we'd have a fragmented group," says Tyco's D'Ambrosia. "By making peace with everyone, we get more expertise -- and more market penetration."
The other key question was whether to use a modulation scheme or to use non-return-to-zero (NRZ) signaling. The group picked NRZ. "We believe we can do this more cost effectively with NRZ," D'Ambrosia contends. Virtually all backplane transceivers today use NRZ, so vendors have plenty of experience with the technology. And it is easier to integrate with VLSI integrated circuits, which use similar signaling techniques internally.
However, that decision could leave startup Accelerant Networks Inc. out in the cold. Accelerant is the only company with a 5-Gbit/s backplane product to date, but it uses a multilevel modulation scheme (see Copper Battles Optics in Backplanes and Accelerant Boosts Backplanes).
HSBI is still in a very early stage of definition, says Jim Tavacoli, Accelerant's VP of marketing, and there is not enough concrete definition available for anybody to assess whether such an approach is going to work or not. Whereas Accelerant's solution, he claims, "has proven performance at up to 6.25 Gb/s on over 50 existing backplanes, some of which were designed to operate at speeds as low as 622 Mhz."
Accelerant is a supporting member of HSBI, he adds, and continues to stay abreast of new developments.
— Pauline Rigby, Senior Editor, Light Reading
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