Bell 202 modem
The Bell 202 - modem is one of the first modem, by the company AT & T has been developed. The half-duplex transmission takes place in one direction at 1200 bps ( bits per second ). Frequency Shift Keying (FSK) is used as the modulation method. A digital "1" is displayed with the frequency 1.2 k Hz (1200 Hz) and a "0" is displayed with the frequency 2.2 kHz (2200 Hz).
Since this modem technology was the first of its kind, the designations Bell 202 compatible or Bell 202 standard were coined.
The ITU V.23 communication standard defines the same type of transmission, but is incompatible with Bell 202 because other signal frequencies are used.
- Highway Addressable Remote Transducer , a standardized, widely used communication system for setting up industrial fieldbuses