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.
(1996-07-22)
Read Also:
- V.22
protocol, standard An ITU-T modem protocol which allowed data rates of 1200 bps. V.22bis doubled this. (2004-07-26)
- V.22bis
protocol, standard V.22 twice. An ITU-T modem protocol which allowed a data rate of 2400 bits per second, twice that of V.22.
- V.23
protocol, standard 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. (2004-07-26)
- V.25
communications, standard A standard allowing an auto-answer modem to determine the correct modulation standard to use. (2001-04-06)
- V.25 bis
communications, standard A cryptic command language for modems. (2004-08-02)