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98 Chapter 4

It provides protection switching.
It aligns on frame boundaries.
It determines performance at the section level.
It performs other associated chores.

Table 4-6 reviews the common rates and interfaces we use in our
daily communications lives. These rates include the common inter-
faces used in an organization for various connectivity solutions.
In Figure 4-12 we see that the use of SONET and SDH equipment
became prevalent in the early 1990s. However, the movement is
away from the older PDH technologies and more toward the instal-
lation of newer SONET and SDH equipment. Within the carrier
communities, the movement is dramatic, with virtually no older
PDH equipment remaining in the pipeline for installation in the
future. This market (PDH) is just about completely gone, with the
synchronous marketplace exploding at a rate that exceeds anyone’s
wildest expectations.

Figure 4-12 25
Market for
SONET/SDH
equipment 20

Billions of $ (US) 15

10

5

0
1988 1990 1992 1994 1996 1998 2000 2002

Old techology SONET/SDH