V.21

V.21

(protocol, standard)
An ITU-T modem protocol for 300 bps two-wire full-duplex communications using Frequency Shift Keying modulation.

All modern modems support both V.21 and the close variant, Bell 103.
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V.21

An ITU standard (1964) for asynchronous 0-300 bps full-duplex analog modems for use on dial-up lines. It uses FSK modulation.
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