10 Synchronous Optical Networks and Synchronous Digital Hierarchy
Mark Matthews
Nortel Ltd.
Goff Hill
GTel Consultancy Ltd.
Introduction
The Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) are standards that were designed for multiplexing together many low-rate digital traffic channels (in particular, 64-kbit/s voice channels) into higher-rate channels so that the low-rate channels can be more efficiently transported around a telecommunications network. SONET is both the forerunner and the North American equivalent of SDH.
SONET and SDH have many similarities, but they use different terminologies. In the following sections, the main differences between the two standards are first described and then, to avoid confusion, ...
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