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54 Chapter 3

Once upon a time, standards were set in North America by the Bell
System, in particular, by AT&T.As the prime carrier for network ser-
vices, AT&T set the rules on how the network operated. In 1958, the
designers at AT&T developed the North American Digital Hierarchy
as a means of delivering high-speed digital communications. This
worked throughout the network because at the time, only one
provider existed. Because there was no competition, AT&T needed
only to satisfy itself on the operation of the network. Although the
North American Digital Hierarchy worked, many limitations also
existed that curtailed the overall operation of the network. One such
problem was in the asynchronous nature of many of the transmis-
sion systems. The industry needed some critical changes in the net-
work to accommodate growth and competition. Moreover, other
changes were underway. In the late 1960s, competition began to
appear in the long-distance network. This competition began to
bring additional constraints inside the network to the surface.
Until recently, signal transmission consisted of voice communica-
tions, dial-up data communications, and leased lines. These varia-
tions all depended on the voice concept of analog communications.
However, modern networks must go beyond just a voice networking
standard and support many different types of signals. These
demands required the development of new standards that used syn-
chronous transmission capabilities throughout. The services also
required openness, including

Multivendor support
Multivendor compatibility
Ease of adding new services when they develop

Enhancements to operation, administration, maintenance, and
provisioning

Midspan meeting capabilities
These needs were not being met at the time because no competi-
tors shared the services and the backbone networks other than Bell.
The changes appeared when the emergence of competition changed
the way the network worked. These requirements led to the devel-
opment of the Synchronous Optical Networking (SONET) standard
in 1984 and ratification in 1988. SONET is a standard developed by