Japan's network evolution relies on SDH-based systems

The commercial introduction of optical transmission systems based on the synchronous digital hierarchy (SDH) systems by Nippon Telephone and Telegraph is discussed. SDH-based systems efficiently multiplex signals, from narrowband telephone and facsimile signals to broadband video signals. All digital sources are synchronized regardless of their signal speed. The transmission system design concept, including the synchronous digital transmission system's modular structure that allows its functions to be freely increased and enhanced, and the SDH-based system deployment are described.< >