Telephone network and ISDN : operation, numbering, routing and mobile service: recommendations E.100 - E.333 / International Telecommunication Union
Telegraph and mobile services operations and quality of service : recommendations F.1 - F.140 / International Telecommunication Union
Message handling and directory services operations and definition of service : recommendations F.400 - F.422, F.500 / International Telecommunication Union
General characteristics of international telephone connections and circuits : recommendations G.100 - G.181 / International Telecommunication Union