Robert Pease
As the demands for faster transmission speed and greater capacity rapidly increase, corporate network managers are eyeing dense wavelength-division multiplexing (DWDM) technology as one solution to increasing their company`s bandwidth. According to market research firm Pioneer Consulting (Cambridge, MA), the growth of DWDM in enterprise networks will triple by the year 2000. One of the first companies to seriously consider using dwdm within the corporate environment is Microsoft Corp. at its campus in Redmond, WA.
Microsoft currently is conducting a trial, expected to run through September, to determine whether the technology has "matured" enough for deployment throughout its facility. The foundation of Microsoft`s Puget Sound ring network in Redmond is a powerful Synchronous Optical Network (SONET) backbone built with 4-fiber bidirectional line-switched rings. With more than 25 trillion bytes of information being transmitted in a single day by its employees, Microsoft wants to gauge the possibility of DWDM technology to replace or augment its current sonet backbone.
"We want to use the trial to get a handle on the integration to the existing environment and operational issues," says Gregg Atkins, Microsoft global networking senior network engineer. "We need to see if it can be integrated seamlessly or if it represents an area in our architecture that we need to work on over time." Four high-traffic buildings within the overall campus were selected for the test, using Lucent Technologies` Wavestar Optical Line System 40G metropolitan equipment. Within this trial network, each fiber will handle 16 wavelengths at a mix of 2.5 gigabits per second, 600 megabits per second, and 150 Mbits/sec. The DWDM system combines the 16 different lasers into one common laser signal, known as "white light," that operates at effectively 16 times the capacity of each individual laser, according to Kathy Szelag, marketing vice president for Lucent`s Optical Networking Group.
In the past, cost has been a significant show-stopper in the deployment of dwdm within enterprise networks that cover short distances, such as a corporate campus. The system being used by Microsoft is fundamentally the same as on a long-haul telecommunications network, notes Szelag. But to reduce costs, several components critical only to long-distance applications have been removed. "You don`t have to sacrifice capacity or reliability," says Szelag. "You`re just not having to spend money on features you don`t need for short distances."
The system differs in other ways, too. "This is a unique system in terms of handling a variety of inputs," says Szelag. "It is capable of handling the type of traffic generated by an enterprise company as opposed to a telephone company." The optical multiplex unit at the input terminal doesn`t require SONET, which is the typical input in a telecommunications system. Instead, Microsoft will have the option of inputting other types of laser signals. For example, Asynchronous Transfer Mode and Internet protocol signals can be input directly without SONET. The transponder can self-adjust to the laser signal. Although Microsoft chose shorter distance requirements, the system has a maximum range of 132 kilometers, says Szelag.
Although Microsoft is testing DWDM as one option in increasing its campus network`s capacity and speed, the jury is still out on what steps the company eventually will decide to take, according to Microsoft`s Atkins. OC-192 (10-Gbit/sec) technology is being considered as one alternative. But Atkins says that with the density of traffic on the campus, OC-192 rings would be used up very quickly, requiring multiple overlay rings to support new and existing traffic.
"I`m caught between two technologies: OC-192 and wavelength-division multiplexing [WDM]," says Atkins. "SONET has a rich OAM&P [operations, administrative, maintenance, and provisioning] standard and allows us a way of maintaining a lot of complexity, and that`s a major benefit. It also provides some good early warning signals for preventing failures and keeping tabs on the health of the network. The trial run on wdm is to find out if it`s mature enough to replace our sonet backbone and still deliver all of the benefits derived from sonet architecture."
Atkins says Lucent was "first in the door" with a solution for Microsoft`s DWDM trial. But should the company decide to move ahead with complete DWDM deployment, Microsoft likely will seek multiple vendors. The company also may conduct other trials of DWDM products involving other vendors before making a final decision.
Once Microsoft is satisfied with its test results, the Redmond campus could see either immediate deployment of DWDM throughout the network or an interim step of employing multiple OC-192 rings. "If we determine that wdm has matured to the point of being able to meet all of our needs and replace the benefits of SONET, we`re ready for it now," says Atkins.
Robert Pease is associate editor of Lightwave magazine. This article is reprinted from the August 1998 issue of Lightwave, another PennWell publication.
