Historical
ANSI C12.21-2006 (R2016)
Protocol Specification for Telephone Modem Communication
Details the criteria required for communications between a C12.21 device and a C12.21 client via a modem connected to the switched telephone network. The C12.21 client could be a laptop or portable computer, a master station system or another electronic communications device.
NEMA: National Electrical Manufacturers Association [nema]