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116 Chapter 5

with DWDM can produce some significant improvements for today’s
technology. An example of this is the fact that some DWDM multi-
plexers can produce up to 240 Gbps on each pair of fibers. This
equates to a call-carrying capacity of up to 3.1 million simultaneous
calls on a single fiber pair. Now many of the carriers have installed

at least 12 pairs of fibers in their backbone networks. Performing the
math yields 37.2 million calls simultaneously on the fiber using cur-
rent technology before more fibers are required. This is obviously
very attractive to the carriers, who would prefer to get more service
on their existing infrastructure rather than installing more glass in
the ground. WDM is particularly useful when congestion begins to
build up on the existing carrier networks. Surely, the equipment is
expensive, but the cost of adding multiplexing equipment or chang-
TEAMFLY
ing it out is far less than digging up the ground to lay more fibers.
The electronics of DWDM multiplexers are rapidly becoming very
cost-efficient.
Using different light wavelengths, DWDM simultaneously trans-
mits densely packed data streams on a single fiber. By combining
DWDM with special amplifiers and filtering equipment on the links,
the carriers can achieve unprecedented throughput on their existing
single-mode fiber. Current technology supports approximately 16
different wavelengths on a single fiber (OC-192 is 10 Gbps; using 16
wavelength produces up to 160 Gbps in each direction). As stated in
the beginning of this chapter, 128 wavelengths are targeted for early
in the new millennium. Table 5.3 is a summary of some of the bene-
fits of the DWDM usage.

Why DWDM?

Clearly, the use of fiber technologies has taken over the industry.
However, the more information that can be generated over a single
fiber, the better the carriers like it. To be specific, before digging up
the ground to lay more fibers, it is far less expensive to use multiple
wavelengths of light on a single fiber.Thus, as carriers seek more uti-
lization on the existing fiber, the incentive is for manufacturers to
continue proliferating this technology.

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