The V.23 standard was an early
modem
The Democratic Movement (, ; MoDem ) is a centre to centre-right political party in France, whose main ideological trends are liberalism and Christian democracy, and that is characterised by a strong pro-Europeanist stance. MoDem was establis ...
standard first approved by
ITU-T
The International Telecommunication Union Telecommunication Standardization Sector (ITU-T) is one of the three Sectors (branches) of the International Telecommunication Union (ITU). It is responsible for coordinating Standardization, standards fo ...
precursor CCITT in 1964.
It specifies
audio frequency-shift keying
Frequency-shift keying (FSK) is a frequency modulation scheme in which digital information is encoded on a carrier signal by periodically shifting the frequency of the carrier between several discrete frequencies. The technology is used for c ...
(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 ...
,
full-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 continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
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 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 French
Minitel
The Minitel, officially known as TELETEL, was an interactive videotex online service accessible through telephone lines. It was the world's first and most successful mass-market online service prior to the World Wide Web. It was developed in Ces ...
service, or the British
Prestel
Prestel was the Brand#Brand names and trademark, brand name of a videotex service launched in the UK in 1979 by BT Group#Post Office Telecommunications, Post Office Telecommunications, a division of the British Post Office Limited#History, Po ...
service.
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 (bit/s), half-duplex. It has separate sets of circu ...
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 is ...
References
External links
the ITU V.23 normalization
Modems
Telecommunications-related introductions in 1988
V.23
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