Electronic Design

Ethernet And PCI Express: A Match Made In...

Ethernet remains the network of choice, but now there are alternatives to running it on the backplane. PLX Technology looks to tunnel Ethernet via PCI Express (PCIe), allowing both protocols to run over a single PCI Express backplane. This should reduce the number of connections, cut down on power requirements, and simplify backplane switching.

The tunneling approach isn’t a general specification yet, but it works with the Reduced Gigabit Media Independent Interface (RGMII) found on most Ethernet-equipped microcontrollers and Ethernet switch chips. PCI Express offers many advantages, including lower cost, lower power (9.8 W for PCI Express versus 37 W for Ethernet), and high performance. Also, PCI Express switches and interfaces are scalable from 1x to 32x connections.

PLX Technology will deliver PCI Express switch chips with RGMII interfaces. The number of RGMII ports will depend on where they will be used. The number and type of PCI Express ports will also vary.

From the Ethernet device’s point of view, the connection looks like a typical Ethernet connection so any protocol can be used. A network of this type may interface with a real Ethernet network. But in many instances, the PCI Express switch will provide the necessary connectivity.

A PCI Express device could handle the tunneling protocol so an RGMII interface wouldn’t be required, but this will require a compatible PCI Express device driver. Likewise, this approach could provide a bridge from Ethernet devices to PCI Express devices.

Ethernet is key to most storage area networks (SANs) with network accessible storage (NAS), iSCSI, and soon Fibre Channel over Ethernet (FCoE) coming into play. NAS boxes provide file server interfaces like NFS and Microsoft’s CIFS. iSCSI is gaining ground as the storage interface for virtual machines now running on the bulk of multicore servers.

NAS and iSCSI use TCP/IP and would work nicely with the PLX tunneling support. FCoE protocol stacks look like iSCSI and NAS. FCoE’s lower level isn’t a routeable protocol, though it may work with the tunneling system. Routing may be less of an issue as FCoE is likely to be used on a local private network where routing is not required.

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