Page 176 - Optical Switching And Networking Handbook

08_200023_CH07/Batesx 1/17/01 8:19 AM Page 161

Optical Networking and Switching Vendors 161

Is There an Alternative in the
House?

The alternative for the carriers is DWDM. This increases the capac-
ity of embedded fiber by first assigning incoming optical signals to
specific frequencies within a designated frequency band and then
multiplexing the resulting signals out onto one fiber. The technology
that enables this high-speed, high-volume transmission is the optical
amplifier.A network using such an amplifier could easily handle ter-
abits of information.
Think of a highway, where one fiber can be thought of as a multi-
lane highway. Now let’s think of only one lane open and barriers on
the rest (like the barrels we are accustomed to seeing on highway
systems).Traditional TDM systems use a single lane of this highway
and increase capacity by moving faster on this single lane. Using
DWDM is similar to opening up the unused lanes on the highway
(increasing the number of wavelengths on the existing fiber) to gain
access to an incredible amount of untapped capacity in the fiber.
An additional benefit of optical networking is that the highway is
blind to the type of traffic that travels on it. Consequently, the vehi-
cles on the highway can be trucks (IP datagrams), tractor-trailers
(SONET), or sports cars (ATM cells). This analogy is shown in Fig-
ure 7-3.
As the demand increases, the market share and the spending will
not slow down for some time to come. In fact, spending in United
States for SONET transport equipment, cross-connects, and DWDM
is expected to increase from $10 billion in 1998 to $24 billion by
2002, and predictions take us out to as much as $45 billion by the
2004. With this growth factor shown in Figure 7-4, one can see why
the manufacturers are so excited.
Starting with DWDM, carriers can grow their networks on
demand in the overall infrastructure. This enables them to add
present-day and next-generation TDM systems. Moreover, DWDM
gives the carriers sufficient flexibility to expand any portion of their
networks—a definite advantage of the technology. Carriers seeking
new and creative ways to generate revenue can benefit from a
DWDM infrastructure while meeting demanding customers’ needs.