Recommendation ITU-T G.978 deals with the characteristics of the optical fibre submarine cables used in Recommendations ITU-T G.973, ITU-T G.973.1, ITU-T G.974 and ITU-T G.977. It covers transmission characteristics of optical fibre submarine cables, optical fibres used in submarine cables, including mechanical characteristics and resistance to the environment and other electrical characteristics. It also covers the transmission characteristics of the single- and hybrid-fibre typeelementary cable sections. Any specific information regarding the characteristics of optical fibre submarine cables are included in the relevant optical submarine system's Recommendations.