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Optical/IP

Backplane Standard Gains Allies

Supporters of the PCI Express Advanced Switching standard piled on the enthusiasm yesterday, with 20 companies joining the Arapahoe Working Group finalizing the standard. New members include EMC Corp. (NYSE: EMC), Huawei Technologies Co. Ltd., and Nokia Corp. (NYSE: NOK).

What could arise is a standard interface usable by switch fabrics and system backplanes. Historically, OEMs haven't bothered standardizing these interfaces, and many continue to use proprietary versions. Advanced Switching could change that, paving the way for more OEMs to use off-the-shelf I/O chips, theoretically saving money and development time.

This won't overtake the entire industry, however. Low-end systems that get by with Ethernet-based backplanes (with standard interfaces such as XAUI) can continue to do so, and Advanced Switching likewise won't alter the proprietary design of high-end boxes such as the Cisco GRS 12000, says Rajeev Kumar, program manager at Intel Corp. (Nasdaq: INTC). But there's an enormous middle tier of boxes whose creators would like a standard interface, he says.

Aside from creating a standard, Advanced Switching has the appeal of using PCI-based hardware -- which, because it's developed for PCs, is cheap and plentiful.

"The PHY layer -- the SerDes -- is the same for both [Express PCI and Advanced Switching]. It's the protocol for handling more complex switching that's added," says Beth Logan, Agere Systems' (NYSE: AGR.A) representative to the Arapahoe technical committee.

PCI Express originated as a PCI successor, providing a serial interface suitable for 10-Gbit/s speeds. Intel first proposed the technology, code-named Arapahoe, in 2001 (see 'Wrap-A-Ho? Wazzat?'); the company then changed the name to 3GIO, then changed it again to PCI Express. Meanwhile, "Arapahoe" has stuck as the name of the working group formalizing PCI Express standards.

But PCI Express is meant for chip-to-chip connections. Advanced Switching tacks on the intelligence for more sophisticated topologies -- namely, the kind you'd find in a backplane or a switch fabric. It also adds intelligence for tailoring quality of service (QOS) or high-availability features.

Agere plans to use Advanced Switching with its PI-40 switch fabric, which already uses a 2.5-Gbit/s serial interface. Advanced Switching would provide an alternative to Agere's proprietary, Sonet-based interface, and it could be used to have the PI-40 chips talk to one another, or to connect them to the backplane.

The storage-networking world is another target for Advanced Switching. "Some of the high-end [storage area networking] systems are moving to a blade environment, and they need to tie those blades together," says Intel's Kumar. Moreover, a SAN's need for high QOS and low latency makes Ethernet a difficult fit for backplanes, he says.

Advanced Switching could likewise find uses in wireless backhaul, as carriers try to create services emulating Push to Talk from Nextel Communications Inc. (Nasdaq: NXTL). "You can't build that capability using Ethernet today. One of the issues is, you have to be able to pass control messages between nodes without a lot of latency," Kumar says.

The Arapahoe Group's Draft 0.95 is out now and contains enough information for companies to start working with pre-standard Advanced Switching implementations. The first formal draft is expected to come out in late September or early October. Believe it or not, that corresponds to the schedule Intel laid out for PCI Express in 2001.

— Craig Matsumoto, Senior Editor, Light Reading

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