Attachments to the public switched telephone network (PSTN) : basic attachment requirements for modems standardized for use on the PSTN: NET 20 / European Conference of Postal and Telecommunications Administrations
Attachments to the public switched telephone network (PSTN) : category II attachment requirements for 300 bits per second duplex modems standardized for use on the PSTN: NET 21 / European Conference of Postal and Telecommunications Administrations
Attachments to the public switched telephone network (PSTN) : category II attachment requirements for 2400 bits per second duplex modems standardized for use on the PSTN: NET 23 / European Conference of Postal and Telecommunications Administrations
Attachments to the public switched telephone network (PSTN) : category II attachment requirements for 1200 bits per second half duplex and 1200/75 bits per second asymmetrical duplex modems standardized for use on the PSTN: NET 24 / European Conference of Postal and Telecommunications Administrations