Page 121 - Optical Switching And Networking Handbook

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106 Chapter 5

In the past few years, several major improvements have been made
in the use of optical fiber communications. In earlier discussions
regarding the use of SONET (see Chapter 3) and SDH (see Chapter
4), the issue of bandwidth surfaced. Not only does the issue of band-
width keep coming up, but more significant is the problem of just

how quickly we consume all the bandwidth that is made available.
No matter how much or how fast we improve our spectrum avail-
ability, newer applications crop up that literally “eat up” all the
capacity available to us. The carriers have installed fiberoptic cables
as the backbone to link their interoffice networks. This creates a
mainstay in their communications infrastructure. Using standard
time-division multiplexing (TDM), their standard is to carry between
2.488 and 9.953 gigabits per second (Gbps) on a single fiber. The rev-
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olution to high-bandwidth applications and the explosive use of the
Internet have created capacity demands that exceeded the tradi-
tional TDM limits. TDM only can operate within the spectrum of the
silicon that drives current technologies. What was once considered
an inexhaustible amount of capacity when fiberoptics was first intro-
duced has literally vaporized.The depletion of the excess capacity we
once had drove a new demand for more bandwidth. To meet this
demand, the use of wave-division multiplexing (WDM) surfaced.
To solve the problem, the use of frequency-division multiplexing
(FDM) with our light-based systems became a topic of research.
What ensued was the ability to introduce various wavelengths (fre-
quencies) of light on the same fiber cable and the resulting increase
in possible throughput. We have seen increases approximate
between 16 and 30 times the original capacities of a single fiber.
These capacities are now being pushed to the limit, with variations
being promised of up to 128 times the capacity of existing fiber tech-
nologies. We also hear of 1000 wavelengths being possible. This
means that the old days of having to replace the in-place fibers with
new technology have been supplanted by newer technology that uses
the in-place fiber, necessitating only a change in the electronics on
the line. We can expect to see these advances provide virtually
unlimited bandwidth without en masse changes in the infrastruc-
ture. The future holds the promise of reduced costs, increased band-
width use, and ease of implementation that meets the demands of
our higher-speed communications.

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