The purpose of this Recommendation is to provide optical interface specifications towards the realization of transversely compatible dense wavelength division multiplexing (DWDM) systems primarily intended for metro applications.

This Recommendation defines and provides values for single-channel optical interface parameters of physical point-to-point and ring DWDM applications (with transmission distance in the range of about 30 km to about 80 km) on single-mode optical fibres through the use of the "black link" approach.

Applications containing amplifiers within the black link are outside of the scope of this Recommendation.

This Recommendation describes DWDM systems that include the following features:

– Channel frequency spacing: 50 GHz and wider (defined in [ITU-T G.694.1]);

– Bit rate of signal channel: up to 25 Gbit/s.

Specifications are organized according to the application codes.