Integrated services digital network (ISDN) : internetwork interfaces and maintenance principles: recommendations I.500 - I.605 / International Telecommunication Union
General maintenance principles : maintenance of international transmission systems and telephone circuits: recommendations M.10 - M.782 / International Telecommunication Union
Maintenance of international sound-programme and television transmission circuits : series N recommendations / International Telecommunication Union
Specifications for measuring equipment : series O recommendations / International Telecommunication Union