Message handling and directory services operations and definition of service : recommendations F.400 - F.422, F.500 / International Telecommunication Union
Telephone transmission quality : series P recommendations / International Telecommunication Union
Telematic, data transmission and teleconference services operations and quality of service : recommendations F.160 - F.353, F.600, F.601, F.710 - F.730 / International Telecommunication Union
Telegraph and mobile services operations and quality of service : recommendations F.1 - F.140 / International Telecommunication Union
Telephone network and ISDN : quality of service, network management and traffic engineering: recommendations E.401 - E.880 / International Telecommunication Union