Recommendation ITU-T G.694.1 provides a frequency grid for dense wavelength division multiplexing (DWDM) applications. The frequency grid, anchored to 193.1 THz, supports a variety of channel spacings ranging from 12.5 GHz to 100 GHz and wider. Edition 3.0 of this Recommendation also includes a flexible DWDM grid and definitions for "frequency slot" and "slot width" that can be applied also in fixed grid applications.