Economical and reliable SDH optical transmission system - Introduction of newly developed module AY

This paper describes a new synchronous digital hierarchy optical transmission system that improves the economy and reliability of NTT's local transport networks. The system has 622 Mbit/s long-span optical interfaces with 80 km repeater spacing at a 1.3 mu m wavelength and 160 km repeater spacing at a 1.55 mu m wavelength. The number of repeaters is remarkably reduced by the optical interfaces, making the networks more economical. This system also supports hitless switching function between line terminating multiplexers to make the transmission lines extremely reliable. The system has forced hitless switching operated manually and automatic hitless switching for unpredictable transmission failures.