V.23

An ITU standard (1964) for asynchronous and synchronous 0-600 and 0-1,200 bps half-duplex modems for use on dial-up lines. It has an optional split-speed transmission method with a reverse channel of 0-75 bps (1,200/75, 75/1,200). It uses FSK modulation.

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(protocol, standard)

V.23 - An ITU-T modem protocol which allowed half-duplex (unidirectional) data transmission at 1200 bits per second with a 75 bps back channel and fall back to 600/75 bps. This was the main standard used for British Telecom's Prestel service.