Page 127 - Optical Switching And Networking Handbook

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112 Chapter 5

Depending on usage of various types, the life cycle of OC-48 was
anticipated to be approximately two years. Clearly, the rapid
increase in Internet access, cellular communications, high-speed
data, and the multimedia improvements were on a collision course
with the capacity of this OC-48 architecture. Choosing to move to a
higher-capacity multiplexing technique in TDM was a definite con-
sideration. This led to the higher-rate multiplexing of the OC-192
level ( 9.953 Gbps), a fourfold increase in the speed and throughput
of SONET networks. Yet, even though such increases were achieved
at the OC-192 level, the initial implementation was with one wave-
length of light.
At the same time, OC-48, using two wavelengths, produced a 5-
Gbps throughput on the same fibers, proving that the technology
could work. Shortly after the introduction of OC-192, strides were
taken to introduce OC-48 running four wavelengths (10 Gbps) or a
single OC-192 using one wavelength.
Shortly after 10 Gbps were demonstrated, the designers began to
experiment with 20-Gbps capacity using eight wavelengths of OC-48
and/or two wavelengths at the OC-192 rate. Now the stage was set to
push the envelope as far as possible. It was only a matter of a few
years before the developers began introducing quantum leaps in
their multiplexing ability. Now, with multiples of OC-48 and OC-192,
the capabilities of fiber-based transmission exceed the wildest imag-
ination. Capacities for the DWDM service are now ranging from 160
Gbps to as much as 400 Gbps. This is the first of many steps we can
expect to see in the near future. Some rumors indicate 128 wave-
lengths of OC-192 (that is, 1.2 Tbps) being possible shortly.
Figure 5-5 shows a variable number of wavelengths being
selected in a WDM system that can carry many different wave-
lengths, exponentially increasing the throughput.
Table 5-1 summarizes the capacities of DWDM today and what
the future may hold. The table shows the level of multiplexing as
well as the possible throughput one can expect for the future. The
table also shows the number of wavelengths on the single-mode
fiber.