Page 239 - Optical Switching And Networking Handbook

10_200023_CH09/Bates 1/17/01 9:45 AM Page 224

224 Chapter 9

Reduced optical signal strength due to cross-talk, attenuation,
and other accumulated impairments

“Creeping” impairments that can slip into the overall
construction and degrade the network

Some added complexity in design
More problematic in monitoring the overall quality of individual
signals running on the wires
Advantages of opaque networks include the following:

They require less overall engineering concerns when they are
being laid out.
They can be engineered with a span-by-span (building block)
approach.
For now, considerable ease of implementation exists for add-drop
multiplexing and multicasting.
Several different approaches will be taken by carriers and manu-
facturers to develop the use of transparency in the network of the
future. This is so because the model is still in its infancy. Given the
cost advantages of transparent networking, we can expect to see
much more emphasis on add-drop multiplexing and increases in
demand for these systems. Some issues have yet to be resolved in the
engineering side of transparent networks, but for moderate and
small networks, the use of transparency in multiplexing, multicast-
ing, and add-drop multiplexing will grow in the near term. Figure
9-7 is a representation of a cost model for add-drop nodes with dif-
ferent configurations. The darker bar on the chart represents a sys-
tem cost based on four add-drop channels of a 16-channel system in
the node. The lighter bar is the cost value of the node based on eight
add-drop channels of a 32-channel system.

DWDM Capabilities

DWDM enables the network to be more powerful and flexible. For
example, optical add-drop multiplexers (OADM) can be installed
between two end terminals on any route. These enable the operator