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PLX defines plan for Ethernet tunnelling in PCIe

Posted: 26 Nov 2008     Print Version  Bookmark and Share

Keywords:Ethernet  PCI Express  backplane-based network  backplane systems 

California-based PLX Technology Inc. has defined a way to run Ethernet over its PCI Express switches, eliminating the need for Ethernet silicon in some backplane-based network and computer systems. The company claims that the approach could slash two-thirds off the power and cost of interconnect chips in such systems.

The so-called Reduced Gigabit Media Independent Interface (RGMII) essentially encapsulates incoming Ethernet traffic over an Express link on a PLX switch. The tunnelling technique consolidates the use on line cards in today's systems of Express, Ethernet and proprietary interconnects.

"There are three networks on these cards now and OEMs want to consolidate them, combining the two control networks into one by running Express with Ethernet tunnelling," said Shreyas Shah, a systems architect at PLX.

PLX borrowed the concept from the Advanced Switching Interconnect, a variant of PCI Express that could encapsulate different protocols but failed to gain market traction. The new technique uses the multi-casting capability in the Express standard as well as its point-to-point flow control features.

The company claims by eliminating Ethernet chips in backplane systems, OEMs can cut interconnect chip costs from Rs.5,704.15 to Rs.1,601.16 ($114 to $32). Power consumption would fall from 37 to 9.8 W, the company claims.

The technique requires PLX to re-spin its silicon, updating content-addressable memories to handle tables for address and I/O mapping. Thus the company does not expect to ship switches with the new interface until 2009.

So far PLX is exploring the concept with two large system makers. "Once we get to a certain point in developing the technology we may push for a standard," said Shah.

Vendors have pushed for backplane standards based on a wide variety of their favourite interconnect protocols including Express, RapidIO and versions of Ethernet. To date Gbit Ethernet dominates as the backplane interconnect of choice, a position that would be hard to unseat according to Joe Pavlat, chairman of the PCI Industrial Computer Manufacturers Group that sets backplane standards.

-Rick Merritt
EE Times

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