The V.23 standard was an early

modem A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulati ...

standard first approved by

ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Commu ...

precursor CCITT in 1964. It specifies

audio frequency-shift keying Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier signal. The technology is used for communication systems such as telemetry, weather ball ...

(AFSK) to encode and transfer data at a rate of 1200

bits per second In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...

half-duplex A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow ...

at 1200 baud (Mode 2), (or at a "fallback rate" of 600 baud, mode 1) for the forward data-transmission channel, and an optional 75 baud backward channel. * V.23 Mode 1 AFSK uses a 1300 Hz tone (F_Z) for ''mark'' (typically a binary ''1'') and 1700 Hz (F_A) for ''space'' (typically a binary ''0''), and a 1500 Hz center frequency (F₀). * V.23 Mode 2 AFSK uses a 1300 Hz tone (F_Z) for ''mark'' (typically a binary ''1'') and 2100 Hz (F_A) for ''space'' (typically a binary ''0''), and a 1700 Hz center frequency (F₀). * V.23 backward channel AFSK uses a 390 Hz tone (F_Z) for ''mark'' (typically a binary ''1'') and a 450 Hz (F_A) for ''space'' (typically a binary ''0''). In some

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a Continent#Subcontinents, subcontinent of Eurasia ...

an countries, (and perhaps elsewhere), V.23 Mode 2 AFSK modulation, (without the backward channel) is used to transmit

Caller ID Caller identification (Caller ID) is a telephone service, available in analog and digital telephone systems, including voice over IP (VoIP), that transmits a caller's telephone number to the called party's telephone equipment when the call is ...

information over POTS lines in the

public telephone network The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local teleph ...

. The 75 baud backward channel was originally envisioned for use in error correction schemes, but V.23 was also widely used in

Videotex Videotex (or interactive videotex) was one of the earliest implementations of an end-user information system. From the late 1970s to early 2010s, it was used to deliver information (usually pages of text) to a user in computer-like format, typi ...

applications where the backward channel was used to send keyboard data in an asymmetrical full duplex scheme in devices such as the

Minitel The Minitel was a videotex online service accessible through telephone lines, and was the world's most successful online service prior to the World Wide Web. It was invented in Cesson-Sévigné, near Rennes in Brittany, France. The service was ...

Related technology

The

BELL 202 The Bell 202 modem was an early (1976) modem standard developed by the Bell System. It specifies audio frequency-shift keying (AFSK) to encode and transfer data at a rate of 1200 bits per second, half-duplex. It has separate sets of circuits fo ...

communications standard defines a similar modulation scheme.

References

External links

the ITU V.23 normalization
Modems Telecommunications-related introductions in 1988 {{telephony-stub

Related technology

See also

References

External links