Approval requirements for data terminal equipment to connect to packet switched public data networks using CCITT recommendation X.25 (1984) interface : NET 2 / European Conference of Postal and Telecommunications Administrations
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 1200 bits per second duplex modems standardized for use on the PSTN: NET 22 / 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