Gigabit Ethernet ventures into the land beyond the LAN

High-speed technology

Users are starting to get into Gigabit Ethernet for the long haul - literally. As Gigabit Ethernet picks up momentum in enterprise LANs, it is also extending to metropolitan-area networks (MAN), connecting buildings or campuses scattered throughout a city. Enterprise users cite the technology's low cost and familiarity as primary reasons for implementing Gigabit Ethernet across MANs and even WANs.

The Gigabit Ethernet specification allows the technology to stretch 5 kilometers from one switch to another, though sources say standard Gigabit Ethernet can actually reach about 10 kilometers with more powerful optics than those specified in the standard. With proprietary hardware and high-quality fiber-optic lines, some vendors claim to extend the technology's reach up to 70 kilometers and farther.

As early work on a 10-Gigabit Ethernet standard gets underway, vendors are pushing for the standard to include specifications supporting MAN and WAN links. At the IEEE's call for interest on 10-Gigabit Ethernet in March, vendors acknowledged the need for the technology in LAN backbones but indicated that it also has to have a future over long distances.

In the meantime, companies lucky enough to have access to dark fiber - that is, fiber-optic lines that have been installed but are not carrying signals - can run Gigabit Ethernet between sites as a backbone network technology. One example is Harris Corp., which wanted to connect its Electronic Systems Sector (ESS) business with the main headquarters across town in Melbourne, Fla. The 5,000 users at ESS would run financial, e-mail and Internet applications over the link to headquarters.

Though Harris' bandwidth requirements weren't high, the low price of Gigabit Ethernet gear was compelling. "It was $35,000 for the whole thing," says Mike Oyler, systems engineer at ESS, which settled on equipment from Foundry Networks. He adds that Fast Ethernet probably would have been even less expensive, but he wanted to ensure the network wouldn't have to be upgraded for a long time. "Why worry about the future?" he says.

Without Gigabit Ethernet services from carriers, users will have to find dark fiber. Carriers usually resell dark fiber, but unfortunately, dark fiber is not available everywhere.

"We can't get dark fiber from here to our new facility, which is 10 miles away," says Marsha Klapperman, senior network engineer at Network Appliance in Redwood City, Calif. The company wants to connect the buildings primarily to conduct file transfers using Network Appliance's network storage devices.

Instead of utilizing a gigabit per second, Network Appliance will have to throttle down its connection to OC-3 (155M bit/sec) or DS-3 (45M bit/sec) over the 10-mile span, Klapperman says.

Carriers, however, are also looking into Gigabit Ethernet for offering services over long distances (NW, April 12, page 1). Companies that are interested include Ameritech, Bell Atlantic, BellSouth and SBC Communications.

Gigabit Ethernet and ATM

Gigabit Ethernet joins other network technologies still widely used in the MAN, such as FDDI and ATM.

Gigabit Ethernet owes its popularity to the market dominance of its fellow Ethernet technologies. Because vendors sell much more Ethernet and Fast Ethernet equipment than token-ring or FDDI gear, Gigabit Ethernet is becoming popular because it is a similar technology. Because so many vendors are making Gigabit Ethernet equipment, competition is pushing down prices.These factors also apply in the MAN, so Gigabit Ethernet's popularity is spilling over into MAN environments.

To its disadvantage, Gigabit Ethernet doesn't have the resilience of other technologies used in this area.

"It's not a terribly fault-tolerant technology," says Mary Petrosky, an independent technology analyst in San Mateo, Calif. ATM was built to travel over long distances and withstand adverse conditions. ATM was also built to carry real-time traffic, such as voice and video.

Time-critical applications really require ATM, says Tim Price, an assistant network administrator at the U.S. Army's Redstone Arsenal in Huntsville, Ala. Redstone conducts weapons tests with pieces of equipment in different locations. To stay synchronized, the equipment uses ATM, Price says.

However, the arsenal uses Gigabit Ethernet over long distances. The installation is spread out over 10 kilometers, and Gigabit Ethernet carries the installation's more conventional LAN applications, such as e-mail. "We couldn't run ATM to everything," Price says. "It's just too expensive."

Others rely on Gigabit Ethernet, even for supporting video traffic. The MAN connecting educational institutions in Spokane, Wash., runs video over Gigabit Ethernet by applying quality-of-service controls to the traffic (NW, July 20, 1998, page 60). Because video is given a higher priority than other traffic, it's guaranteed to get through when the links are overloaded.

One big cost associated with Gigabit Ethernet over a MAN is in the fiber itself. The Spokane schools, for instance, spent four times as much on laying dark fiber than they did on Gigabit Ethernet equipment from Packet Engines. While pricing for Gigabit Ethernet services hasn't been set, current transparent LAN services cost anywhere from $750 to $2,000 per month.

For the most part, the factors in deciding between using Gigabit Ethernet or ATM in the MAN are the same as the factors in deciding whether to use one transmission technology or the other in LAN backbones. Users who care more about costs will often choose Gigabit Ethernet, and those who care more about real-time traffic will often choose ATM.

So many choices

It is still undetermined which technology will prove more popular with users. Service providers are getting hit with many options when it comes to transporting data over the MAN and WAN, Petrosky says. In addition to Gigabit Ethernet and ATM, service providers can choose IP over SONET or Multi-protocol Label Switching. Transparent LAN services providing Ethernet, Fast Ethernet and FDDI in MANs are also available.

Gigabit Ethernet is very much the newcomer to this environment. Most early enterprise adopters started testing Gigabit Ethernet gear in 1997, with implementations ramping up last year (NW, July 20, 1998, page 1).

"I have a feeling we're going to see some experimentation with Gigabit Ethernet," Petrosky says. "People will play with this and see what will fly."