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It's a four-way battle for the backplane

Posted: 27 Mar 2007 ?? ?Print Version ?Bookmark and Share

Keywords:Ethernet? Infiniband? PCIe? RapidIO? backplane?

The race to the backplane is heating up.

Competing silicon vendors are gearing up chips to put Ethernet, Infiniband, PCIe and RapidIO in pole position for next-generation servers and communications systems that link multiple processing cards over a backplane. System makers say that while Ethernet looks like the long-term winner, Infiniband and RapidIO will have significant niches, at least in the near term. But all sides say it's still early days in a race where anything can happen.

IDT Corp. rolled out a chipset specifically designed to put 2.5GHz Express in the backplane. It leapfrogs existing offerings from PLX Technology, Pericom Semiconductor and NEC Electronics.

To stay ahead of the pack in raw bandwidth, Mellanox Technologies Ltd later this year will release quad-data-rate versions of Infiniband chips. They will use four 10Gbps per-lane links to create a 40Gbps interconnect.

The chip efforts aim to grab design wins in an increasing number of systems that use backplanes. Such systems lower costs by leveraging open standards and third-party adapter cards while also increasing ease of use and flexibility.

A handful of chipmakers are working quietly on a new serial 10GbE specification dubbed KR. The spec, part of the IEEE 802.3ap effort on backplane Ethernet, is in its final stages, though silicon may not ship until next year.

"The big architectural change is the move to virtualization and shared I/O," said Jack Regula, chief technology officer at PLX Technology Inc.

Hot question
The question of whether Ethernet, Infiniband or PCIe is the better backplane technology is a hot one. Mike Krause, an interconnect specialist in Hewlett-Packard Co.'s X86 server group, suspects the long-term winner will be determined by which technology winds up integrated in mainstream multicore processors, probably before 2012.

"This is the big multibillion-dollar question: 'Do you put Express, KR or what into the processor, and when?' " said Krause. "Neither AMD nor Intel is showing anyone their plans yet, but they will follow the volume."

Sun Microsystems Inc. already integrates GbE and 10GbE in its Niagara processors. In addition, "IBM has hinted about integrating I/O in the Power7," Krause said.

The use of interconnects should improve companies' ability to offer hardware virtualization, since CPUs would not need to incur the delays of going to external chips to handle I/O requests. Ethernet is a better bet for integration, however, because its newest variant, KR, provides 10Gbps per lane. Express, by contrast, could require five lanes or more for as much throughput, pushing up the chip's pin count.

KR has its own disadvantages; it "is not a perfect spec," admits Krause. But by 2010, design and process improvements could make it a better candidate for CPU integration in terms of low power and clean signaling. "Our assumption is 10G Ethernet replaces Gigabit Ethernet in the 2010-and-beyond time frame," Krause said.

Communications engineers agree. For example, the recently merged Alcatel-Lucent is consolidating its many systems into a few central platforms to lower its costs and speed time-to-market. "These platforms try to address a wide range of applications and generally follow Ethernet signaling in the backplane and ATCA packaging. That represents 80-90 percent of our needs," said Charles Byers, a Bell Labs fellow and consulting member of the technical staff at Alcatel-Lucent.

Indeed, "I believe pretty strongly Ethernet will win," said Mike Coward, chief technology officer at Continuous Computing, which makes cards and systems for end users and OEMs such as Alcatel-Lucent. "Infiniband, Express and RapidIO are great technologies and will find use on line cards, but the backplane will be dominated by Ethernet." Continuous is already expressing support for KR, even though it has not seen anything more than paper plans for KR chips so far. "As the silicon becomes available, we will certainly adopt it," Coward said.

Early player
Infiniband got into the backplane race fast and early with a 24-port chip offering 20Gbps per port. The product shipped in late 2003 from Mellanox. The company, currently the only one to offer merchant Infiniband chips, will roll out support for 40Gbps Infiniband and KR this year.

Infiniband has gained some traction in blade servers from Dell, HP, IBM and Sun. In the comms space, it has not been as successful. One board maker, Diversified Technology Inc. ships a Xeon card for Infini band systems. And an Asian OEM will ship an Infiniband-based AdvancedTCA system later this year, said Thad Omura, VP of product marketing for Mellanox.

For some communications suppliers, Infiniband's main drawback is business-related. Because Mellanox is the sole supplier of Infiniband switch chips, the level of innovation, price competition and just plain confidence in the technology is lower than with other approaches.

By contrast, a few companies are making switches to put RapidIO in the backplane. RapidIO is designed to work not only with control-plane processors like the X86, but also with DSPs and network processors handling data-plane functions.

"There are some places Ethernet can't reach without a lot of cost or development pain in areas such as QoS and 10Gbit TCP/IP termination. In these areas, we like RapidIO," said Dave Wickliff, distinguished member of the technical staff for Alcatel-Lucent.

In addition, the RapidIO trade group is on the cusp of launching a version 2.0 spec that bolsters the QoS and flow control features the technology uses in backplanes. The spec also doubles RapidIO's physical data rate from 3.125GHz to 6.25GHz.

That said, "Infiniband actually has a really strong storyespecially in the next one to three years, because it has the best price/performance," said Krause of HP. But "if Ethernet goes into the processor in 2010 or 2012, that's a firm end date to their story."

Express in slow lane
Meanwhile, a smattering of small chip makers are backing Express in the backplane and Sun is using Express in the server blades it launched in 2006. Many say the technology is the least likely to have a significant play in the backplane, however, due to its design shortcomings. For example, Express lacks memory protection and offers weak congestion-management features compared with Ethernet and Infiniband. And its PC-architecture heritage chafes comms engineers.

"I'd prefer to have Ethernet in the backplane rather than Express, because Ethernet has much better survivability," said Krause.

Nevertheless, the chipset that IDT will release this week is specifically aimed at putting Express in the backplane of computer and comms systems. The company says it is working with a number of OEMs, including one in Asia, that will be the first to release an AdvancedTCA-based system using Express. "We've been working with a number of customers in servers, storage and communications companies that are going to adopt Express as their systems interconnect," said Matt Jones, a division marketing manager for IDT.

- Rick Merritt
EE Times

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