Agencies see the light

As bandwidth demands rise in metropolitan-area networks, a growing number of agencies are beginning to embrace Dense Wave Division Multiplexing (DWDM) technology to add highly scalable bandwidth capacity to their networks at a fraction of the cost of adding fiber-optic cable.

DWDM was known simply as Wave Division Multiplexing (WDM) in 1995, when long-distance carriers began using it. As they exhausted the capacity on installed fiber-optic cable, carriers began to deploy DWDM, which uses denser wavelengths to pack more bandwidth within the existing cable — at one-tenth the cost of digging up streets and laying new fiber cable. Now, even large enterprise customers such as federal agencies are starting to buy and deploy their own DWDM equipment.

"DWDM puts multiple wavelengths on a single pair of fiber to increase capacity," said Bob Azzi, Sprint's vice president of engineering. Fiber-optic cable is typically deployed in pairs, with one transmitting and the otherr eceiving. "There were only four wavelengths in 1995. That has increased to 96 wavelengths and higher."

The fast-growing number of wavelengths results in part from higher-capacity DWDM-based optical components from such companies as Ciena Corp. and JDS Uniphase Corp. Ciena manufactures the MultiWave CoreStream, an intelligent optical multiplexer that is ubiquitous on the Sprint network and transmits 96 wavelengths on one fiber. "Next year we'll transmit 160 channels," said Denny Bilter, Ciena's senior director for marketing.

Because DWDM is transparent to the user, most people are unaware of its prevalence. "We've got 27,000 miles of fiber, and every mile of it has DWDM," said Woody Sellers, director of Defense Department programs at Sprint's Government Systems Division.

The Defense Information Systems Agency network is one of many that dependon Sprint's, AT&T's and WorldCom Inc.'s use of DWDM. "We order point-to-point circuits provisioned on top of a carrier infrastructure that makes use of DWDM," said David Mihelcic, chief executive engineer for DISA Network Services.

All the long-haul networks and many metropolitan networks use DWDM. WDM, which costs less but doesn't deliver the same performance, is still around, but is usually limited to metropolitan or campus networks.

When deciding whether to use DWDM or WDM, everything depends on the application, said Ron Kline, senior analyst for long-haul and metro transport and optical networks services in North America at market research firm RHK Inc. "If it's Internet access for the Department of Agriculture, then DWDM isn't necessary. But if you are running a high-speed line for the DOD, thenit's absolutely critical," he said.

Those with high bandwidth requirements concur. "Today, nothing competes with DWDM," Mihelcic said.

DWDM also offers other benefits. "Because DWDM is based on the [International Telecommunication Union] grid standard, interoperability is easier when you use DWDM," said Fady Masoud, senior manager of product marketing at Nortel Networks Ltd.'s metro optical products division. "Plus, there are more DWDM installed systems than WDM."

To even consider using DWDM, an agency needs to have a fiber network, Mihelcic said.

That is why the Transportation Department has been able to start using DWDM. "We had the foresight 12 years ago to put dark fiber in place. It's paid for itself 100 times over," said Ted Oliver, DOT's director of telecommunications operation at the Transportation Administration Service Center. Dark fiber is fiber-optic cable without the electronics, such as the multiplexers and amplifiers.

When Oliver saw the cost of DWDM equipment dropping this year, he discovered that leasing additional bandwidth from a carrier was more expensive than activating, or lighting, DOT's dark fiber. Using an existing contract between DOT and GTE Corp. for operations, maintenance and support of a telephone system, Oliver decided to employ Nortel's OPTera Metro 3500 intelligent multiplexing platform (a product used under the contract).

The OPTera Metro 3500 combines in one platform the functionality of multiple network elements, such as DWDM, Ethernet, Synchronous Optical Network (SONET) and Resilient Packet Ring, Masoud said. Support for those multiple protocols is one of the benefits of DWDM.

DOT replaced Cisco Systems Inc. routers with OPTera Metro 3500s. Then the agency placed its Cisco routers on the outer edges of its network soit wouldn't lose the investment. "We expanded our coverage by reusing our Cisco 7500 high-end routers and increased capacity by adding the Metro 3500s," Oliver said.

But those weren't the only requirements that Oliver wanted to meet. He also sought to achieve high availability for the department's storage-area networks and IP television network, as well as provide a backup system for e-mail. "The biggest end-user benefit right off the bat was increased bandwidth," Oliver said. "To download files takes only seconds now. Plus, video used to need [a television] and coaxial cable and now it comes right to the desktop."

After six months of planning and design, DOT's rollout went smoothly.S ome of the time was spent learning about optical technology and integrating it with existing network technology, said Joe Matsuki, DOT senior network engineer.

"Our biggest challenge was making sure the single-mode fiber we were using tested to Nortel's specifications for optical networking," Matsuki said. Because the DOT fiber was "10 to 12 years old, we weren't sure if the new optical equipment would work on [it]. We had to change interfaces and other things, but it tested out and worked well for us."

Today, vendors are busy building the parts for a purely optical DWDM network. "This is an approach many believe will be better than SONET," Mihelcic said, because it will make it easier to establish and manage an end-to-end circuit.

It will be some time before all-optical networks show up, said Jeff Wild, vice president of marketing at JDS Uniphase. But enthusiasts see all-optical DWDM networks on the horizon, deployed even more widely than they are now.

"DWDM came from the long haul and has now made its way into the metro network," said Joe Padgett, senior director of marketing for Nortel's metro optical products division. "We've developed DWDM highways over the years, and now we're building the off and on ramps to provide more access. The fiber we are rolling out on secondary streets is getting closer to the endu ser. Eventually, we'll drive DWDM right to the desktop."

Gerber is a freelance writer based in Kingston, N.Y.