Specification primes Gigabit Ethernet pump

After two and a half years of painstaking committee work by some of the network industry's brightest lights, the IEEE in September ratified the 802.3z Gigabit Ethernet standard.

Network managers beset with data traffic jams now have a new class of simple, affordable high-performance switches, routers and servers that can be used in LAN backbones.

Networks can now move traffic at 1G bit/sec with an easy upgrade of their 100M bit/sec Fast Ethernet links. Network managers can make their 10M bit/sec Ethernet desktop connections 10 times faster with switched, full-duplex Fast Ethernet.

This new performance comes with a minimal amount of investment, pain, training and reconfiguration of existing hardware and applications. Gigabit Ethernet takes advantage of the frame size and format of other Ethernet varieties. It also takes advantage of the same applications, management tools, configuration, installation and troubleshooting procedures Ethernet network managers already use.

Gigabit Ethernet encompasses full-duplex media access control, and the classic carrier-sense multiple access with collision detection MAC. While most Gigabit Ethernet implementations will take advantage of the contention-free access and flexible topologies permitted by full-duplex operation, the 802.3z Gigabit Task Force decided to also extend the CSMA/CD MAC to work at 1G bit/sec.

The Gigabit Ethernet specification defines support for multimode fiber-optic links at distances up to 260 meters using 62.5-micron fiber and 550 meters using 50-micron fiber. The specification also defines longer distances using higher cost components, spanning 440 meters on 62.5-micron fiber, 550 meters on 50-micron fiber and up to three kilometers on single-mode fiber. In addition, 802.3z includes a specification for a transceiver technology referred to as 1000BASE-CX, which supports shielded copper cable spanning 25 meters.

The Gigabit Ethernet specification appropriates much technology from the ANSI Fibre Channel standard. In fact, it uses the same code set.

In addition to providing more bandwidth, the Gigabit Ethernet standard supports a new breed of products that can route traffic among different networks at gigabit wire speed - or 100 times faster than traditional software-based routers.

In fact, all of today's internetwork technologies are fully compatible with Gigabit Ethernet, just as they are with conventional Ethernet and Fast Ethernet.

Compatibility and bandwidth are essential, but what ultimately counts is what you can do with the technology. With Gigabit Ethernet, network managers can now accommodate servers and desktops running increasingly complex applications with bigger appetites for bandwidth. These include data-intensive applications in science, engineering and medicine. Bigger bandwidth also makes room for multimedia Web traffic, mixed media conferencing, video, voice over IP and distance learning.

Even with Gigabit Ethernet's inherent benefits, plus the ratification of the standard, choosing among the myriad Gigabit Ethernet products poses a challenge to network managers. When shopping for switches, uplink/downlink modules, network interface cards, routers, interfaces and buffered distributors, consider interoperability guarantees. Ask if the vendor participated in the Gigabit Ethernet Consortium's interoperability trials at the University of New Hampshire. Does the vendor certify its interoperability with other vendors' goods?

Also question whether the product is truely gigabit-scaled. Some vendors have tacked Gigabit Ethernet interfaces on switches and routers that were really designed to accommodate 10/100M bit/sec Ethernet nodes. You'll know these products by their aggregate switching capacity of 2G or 3G bit/sec.

For a sound network infrastructure, look instead for an industrial-strength box with an aggregate switching and routing capacity measured in multiples of 10G bit/sec and tens of millions of packets per second.

And beware of products introduced before early 1997, when an implementable draft standard first became available.

Network managers should also be aware of Gigabit Ethernet's limitations - chiefly that any link over 550 meters requires single-mode fiber, which may require upgrades to cabling infrastructure. This limitation isn't due to the optical power of Gigabit Ethernet, but to modal bandwidth, the nature of fiber optics.

Even as the industry ponders Gigabit Ethernet to the desktop over Category 5 unshielded twisted pair wiring, experts need to start looking at backbone connections measured in multiples of 10G bit/sec and a switching infrastructure capable of accommodating multiples of 100G bit/sec to handle bandwidth demands.

There is also a need to further look at optical technologies that extend Gigabit Ethernet links beyond the current limit of five kilometers and into the neighborhood of 100 kilometers, perhaps using Dense Wave Division Multiplexing. This advance would present compelling opportunities for metropolitan-area networks and WANs.

Review and buyer's guide: Gigabit Ethernet switches
We look at several models and let you compare specs for 15 of them. Network World, 10/19/98.

More Gigabit Ethernet resources

Ruby is vice president, product marketing, of Lucent's Enterprise Infrastructure Products Group in Concord, Mass. He can be reached at (980) 582-8500.