April 03, 2001, 12:22 PM — The self-evident truth about fiber infrastructure is you can never have enough. Spare fiber in your infrastructure today will run out tomorrow. The result is fiber exhaust, which occurs when demand exceeds the availability on your backbone fiber.
The most obvious solution for fiber exhaust is to install additional fiber. But the costs associated with pulling fiber can be substantial, and saying "no" to those who want new applications on your infrastructure can be a career-ending move, while removing older applications on your network to make room for the newer ones won't win you any popularity contests.
Take heart. Wave division multiplexing (WDM) can rescue you. Prior to WDM, a single light beam was used per fiber strand. By contrast, WDM uses many different colors (called lambdas or channels). Each lambda carries an individual optical signal providing the same bandwidth per channel (approximately 2.4G bit/sec with most of today's fiber) as a single light stream.
The more channels, the more bandwidth you can get out of a fiber pair. Generally, WDM provides up to eight channels per fiber pair. This is equivalent to adding seven additional dark fiber strands. Even better news comes in the form of dense wave division multiplexing (DWDM), which supports up to 40 channels today and promises even more tomorrow.
Like many enterprise networks, West Virginia University's fiber infrastructure teeters on the edge of fiber exhaust. Therefore, the university's Advanced Network Applications Lab was charged with evaluating DWDM equipment.
While some established vendors bowed out of our evaluation, Alcatel, Cisco, iTouch Communications (formerly NBase/Xyplex) and Nortel Networks provided us with DWDM shelves. DWDM products are called shelves because they are not really routers or switches. They operate more like intelligent optical patch panels.
Nortel's OPTera Metro 5200 earned the Network World Blue Ribbon Award, because it offered more features, was more resilient and had enhanced management over its competitors. However, the other three boxes were not that far behind the OPTera -- they performed well and provided decent management capabilities.
DWDM may be new to the enterprise scene, but carriers have used it for quite some time to provide a cost-effective cure for fiber exhaust in their own networks. The maturity of these products demonstrate that fact.
Enterprise test criteria
DWDM shelves are strictly Layer 1 devices, meaning they don't really route or switch data packets. For this reason, they can't be measured by the same performance metrics that we would apply to a router or switch. Measurements like packets per second, buffer allocations, back plane speed and processor performance are not relevant in the optical world. Therefore, our tests measured each product's performance based on the following criteria: