Page 71 - Optical Switching And Networking Handbook

04_200023_CH03/Batesx 1/17/01 9:42 AM Page 56

56 Chapter 3

Equipment

Line coding
Maintenance
Provisioning

Multiplexing
Administration
The carriers (local and long-distance providers) were frustrated
with the proprietary nature of the industry because of interoper-

ability problems, sole-source vendor solutions (which held the carri-
ers hostage to one vendor), and cost issues. These carriers
approached the standards committees and demanded that a set of
operational standards be developed that would allow them to mix
and match products from various vendors. In 1984, a task force was
established to develop such a standard. The resulting standard
became SONET.

TEAMFLY
The North American Digital

Hierarchy

The North American Digital Hierarchy is a set of standards estab-
lished for the telecommunications industry in North America. Three
countries supported this set of standards initially—the United
States, Canada, and Japan. These three counties adopted sets of
multiplexing and operating speeds that satisfied the communica-
tions networks at the time. The digital signals accepted and adopted
1
included DS-0, DS-1, DS-2, and DS-3.

DS-0

When a user makes a call on the PSTN, his or her voice is filtered
down to a 4-kilohertz (kHz) analog signal. It is then sampled at 8,000
times per second (the clock rate). The sampling technique creates a

1 DS-2 is defined but not widely used anymore.

®
Team-Fly