General maintenance principles : maintenance of international transmission systems and telephone circuits: recommendations M.10 - M.782 / International Telecommunication Union
Maintenance of international telegraph, phototelegraph and leased circuits : maintenance of the international public telephone network: maintenance of maritime satellite and data transmission systems: recommendations M.800 - M.1375 / International Telecommunication Union
Specifications for measuring equipment : series O recommendations / International Telecommunication Union
Telephone transmission quality : series P recommendations / International Telecommunication Union