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 Comm ...
precursor CCITT in 1964.
It specifies
audio frequency-shift keying (AFSK) to encode and transfer data at a rate of 1200
bits per second,
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 (F
0).
* 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 (F
0).
* 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 subcontinent of Eurasia and it is located entirel ...
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 i ...
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 w ...
.
Related technology
The
BELL 202 communications standard defines a similar modulation scheme.
See also
*
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 i ...
References
External links
the ITU V.23 normalization
Modems
Telecommunications-related introductions in 1988
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