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Backplane Ethernet standards push

Posted: 01 Sep 2004 ?? ?Print Version ?Bookmark and Share

Keywords:backplane ethernet? ethernet? phy? ieee? dsl?

The backplane fabric is the heart of any modular-computing or networking platform. So it should not be surprising that there is growing interest in the work of a new IEEE Study Group, formed earlier this year as part of the IEEE Working Group 802.3, that is trying to define the scope and objectives of a backplane Ethernet project.

Fabric redundancy and fail-over mechanisms improve robustness, while congestion-management algorithms and differentiated classes of service allow the system to provide guarantees for latency, latency jitter and data loss. Also, a scalable fabric allows the system to grow with the demand for bandwidth.

Ethernet currently serves as the backplane fabric in many applications and is being considered for several future ones. It can be used everywhere from blade server platforms to enterprise switches and routers, in addition to Internet Protocol-DSL access multiplexer or wireless-access platforms. Features such as resiliency and congestion management, however, are handled in a proprietary and application-specific manner.

The standardization of backplane Ethernet brings with it several advantages. Standardization promotes multivendor interoperability, broadening the selection of components such as traffic managers and switches and allowing optimization of system design by leveraging the strengths of different suppliers. The value is enhanced with the advent of standards-based modular chassis, such as those defined by the PCI Industrial Computer Manufacturers Group (PICMG). The backplane Ethernet standard would permit a user of a modular platform to purchase a server blade from Vendor A, a storage blade from Vendor B and a networking blade from Vendor C and plug them into a standard chassis with full confidence that they would work together.

Examples of standards-based backplane Ethernet exist today. PICMG has defined a form factor, data plane interconnect and other core features for a modular networking and computing chassis. Furthermore, it has defined adaptations of Ethernet physical-layer (PHY) standards for use over the data plane.

The fact that such standardization efforts are underway justifies an IEEE 802.3 initiative to study backplane Ethernet. IEEE 802.3 is the body responsible for creating international standards for Ethernet, defining value-added extensions to the data link layer protocols and defining new PHY variants. An IEEE 802.3 standard will guarantee interoperability with Ethernet standards and bring significant expertise to the problem.

The definition of a backplane fabric is a large and multidimensional problem that is best solved incrementally. With this in mind, the backplane Ethernet study group has focused on PHY aspects.

The PHY requirements identified by the backplane Ethernet study group include support for a 40-inch PCB backplane with two connectors and use of low-cost materials.

The study group also aimed to define full-duplex links operating at speeds of 1Gbps and 10Gbps per lane, where a lane consists of a differential pair in the forward direction and a separate differential pair in the reverse direction. The 1Gbps variant may not vary significantly from the standing PIC-MG definition, but the 10Gbps upgrade path is a new area of study.

Currently, solutions based on NRZ and the PAM-4 modulation formats have been proposed for the 10Gbps problem.

The study group is also considering a means to automatically negotiate between the 1Gbps and 10Gbps speeds. This would allow plug-and-play backward compatibility with current-generation 1Gbps components.

In March, the study group formally asked IEEE 802.3 to form a new standards project for backplane Ethernet. As an official standards project, the group can begin to evaluate proposals and aim to have a baseline specification by the end of this year.

- Adam Healey


IEEE Backplane Ethernet Study Group

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