Analysis: Get ready for 10-gigabit Ethernet

Soon, 10-gigabit Ethernet is coming to a network near you, and it will change the way networks are built. While historically Ethernet has been used as an access technology, 10-gigabit Ethernet promises to be the simplest, fastest and most cost-effective aggregation and backbone network technology.

This flavour of Ethernet uses the IEEE 802.3 Ethernet media access control (MAC) protocol, frame format and frame size. 10-gigabit Ethernet is full duplex, just like full-duplex fast Ethernet and gigabit Ethernet, and thus has no inherent distance limitations.

Because 10-gigabit Ethernet is still Ethernet, it minimizes the user’s learning curve by maintaining the same management tools and architecture.

While some details are still being worked out with the IEEE’s 10-gigabit Ethernet Task Force, that group has achieved consensus on the scope and purpose of the standard, as well as on many of the technical details. In contrast to previous Ethernet standards, 10-gigabit Ethernet is targeting three application spaces: LANs, WANs and metropolitan-area networks (MAN).

To address these applications, most of the task force’s work involves defining appropriate physical layers (PHY). The PHY defines the electrical and optical signaling, line states, clocking guidelines, data encoding and circuitry needed for data transmission and reception. Contained within the PHY are several sublayers that perform these functions including the physical coding sublayer and optical transceiver or physical media dependent (PMD) sublayer for fibre media.

LAN applications include server interconnect for clusters of servers, aggregation of multiple gigabit Ethernet segments into 10-gigabit Ethernet downlinks and switch-to-switch links for very high-speed connections between backbone or data center switches. The PMD sublayer transforms the incoming stream of changing voltages that represents the data into light pulses so that the data can be sent across fibre-optic media.

Various PMDs have been proposed for the campus and building backbone application, including a PMD based on wavelength division multiplexing that supports installed multimode fiber backbones by transmitting, muxing and demuxing upon reception of four optical wavelengths across one 62.5 micron multimode fibre pair up to 300 meters in length.

10-gigabit Ethernet will also be used for MANs. Here the distance goal of the task force is to reach at least 40 kilometres over single-mode fiber, with the 1550 nanometer serial laser PMD proposal reaching up to 80 kilometers over existing single-mode fiber. With such 10-gigabit Ethernet technology, service providers will be able to build simple Ethernet networks with Layer 3 and Layer 4 switches over dark fibre without SONET or ATM and provision high-speed 10/100/1000Mbps services at low costs.

The task force has defined an optional PHY that can interface with the existing WAN SONET infrastructure. The IEEE goal is to define a SONET-compatible PHY that will operate at a data rate compatible with the payload rate of OC-192c/SDH VC-4-64c. This SONET-compatible interface allows 10-gigabit Ethernet switches and routers to attach to SONET access equipment and use the SONET infrastructure for Layer 1 transport.

While customers will see prestandard 10-gigabit Ethernet products later this year, the IEEE task force does not expect the standard to be completed until March 2002. A key milestone for the effort will be the creation of a first draft by September, which will be reviewed at the task force’s meeting in November.

With 10-gigabit Ethernet, network managers will be able to build LANs, MANs and WANs using Ethernet as the end-to-end Layer 2 transport. In terms of physical media, 10-gigabit Ethernet will support distances of 100 meters to 300 meters on multimode fibre and more than 40 kilometres on single-mode fibre. Long-distance reach on single-mode fibre enables network managers to build simple, low-cost metropolitan-sized networks with Layer 3 and Layer 4 switches and 10-gigabit Ethernet backbones.

Tolley is a product manager at Cisco Systems Inc., vice-president of the 10-Gigabit Ethernet Alliance, member of the Gigabit Ethernet Task Force and member of the Ethernet Working Group. He can be reached at [email protected].

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