• United States
by Joel Goergen, special to Network World

Gigabit Ethernet backplane standard eyed

Jan 09, 20063 mins
Network Switches

Ever-increasing volumes of traffic strain the capacities of computing and communications gear. Boosting port speeds from 100Mbps Ethernet to 1Gbps Ethernet – and now to 10Gbps Ethernet – on servers, storage systems, switches and routers, for example, means the backplanes on those devices must be scaled accordingly.

Many network hardware vendors have implemented Ethernet as their backplane technology, but not in a standardized fashion. Recognizing the potential cost, time-to-market and management benefits a standard could provide, the IEEE’s 802.3ap Task Force is defining a standard for 1Gbps and 10Gbps Ethernet backplanes. Now in draft form, the standard is slated for completion in November.

A system’s backplane acts as a highway for communication between the boards and subsystems that make up a complex device, such as a router or a server blade. A standard Ethernet backplane will allow IT workers to mix and match server blades from various vendors in the same chassis. In addition to providing interoperability, 802.3ap will drive the development of standardized components that will enable vendors to bring next-generation products to market more quickly and at lower cost.

The 802.3ap Task Force is working to define the operation of Ethernet over copper traces embedded in board material that make up today’s backplanes. Specifically, the task force will define new physical layers and allow for backplanes up to 3.3 feet.

Physical layers of 1Gbps and 10Gbps are being defined, with two variants of the 10Gbps backplane: parallel and serial. The parallel variation, the common design on backplanes, splits the 10Gbps signal into four lanes of 3.125Gbps each. The serial variation defines one lane at a full 10Gbps. Preventing signal degradation at the higher frequency levels in the serial variation requires a higher-performance backplane that can maintain a quality signal for a greater frequency range.

The 802.3ap specification will preserve well-defined aspects of 802.3 Ethernet, including the frame format at the media access control (MAC) client/service interface and the minimum and maximum frame size. By conforming to the 802.3 MAC, the proposed backplane standard will be consistent with other 802 standards, including 802.1D (Spanning Tree protocol for bridging), 802.1Q (virtual LANs) and 802.1f (management information).

Compliance to 802.3ap will be measured via the electrical building blocks that make up a backplane – transmitters, receivers and the channels in between them. In particular, the task force is looking to define precise specifications for the serializer/deserializer integrated circuits that implement the transmitter and receiver functions.

Backplanes are complex to design and engineer. With 802.3ap in place, vendors will have the option to purchase a standard Ethernet backplane, making it possible for them to bring affordable, high-performance products to market quickly and potentially opening the market to more players.

Enterprises are expected to benefit from a wider selection of products, and the flexibility to mix and match boards and backplanes from various vendors. Broad availability of standard components are expected to reduce prices of network devices.

Management mechanisms defined for 802.3ap-compliant serializer/deserializer chips are expected to make it easier to debug standard Ethernet-based backplanes. Enterprises will be able to quickly identify whether a board or the backplane is responsible for a dropped packet, for example.

Although a backplane specification may seem esoteric to some IT managers, 802.3ap offers cost, flexibility and management benefits that make it worth tracking.

Goergen is vice president of technology and chief scientist at Force10 Networks. He can be reached at