Recommendation ITU T G.977 is concerned with the system performance and interface requirements of repeatered optical submarine systems using optical line amplifiers (OFAs) as a line repeaters. It covers the aspects related to single wavelength systems (SWS), wavelength division multiplexing systems (WDMS) and dense wavelength division multiplexing systems (DWDMS). The physical implementation of optically amplified fibre submarine systems is considered in Annex A. This edition of the Recommendation introduces a new power budget template for the implementation of coherent systems.