Bell 212A

The Bell 212A modulation scheme defined a standard method of transmitting full-duplex asynchronous serial data at 1200 bits per second (bit/s) over analogue transmission lines. The equivalent, but incompatible ITU-T standard is V.22.

Device
The Bell 212 Dataset is a 1979-vintage modem used for communicating over telephone lines at 300 or 1200 bit/s. The 212A standard provides for the ability of a modem to auto-answer a ringing phone.

Usage
The Bell 212A scheme was the most common standard used for 1200 bit/s transmission on US data networks such as CompuServe during the period that dial-up Internet access was the norm (1980s and 1990s).