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
General recommendations on telephone switching and signalling : functions and information flows for service in the ISDN: supplements: recommendations Q.1- Q.118 bis / International Telecommunication Union
Specifications of signalling system No. 7 : recommendations Q.930 - Q.940 / International Telecommunication Union