ITU V.23
Encyclopedia
The V.23 standard was an early modem
standard approved by the ITU
in 1988. It specifies audio frequency-shift keying
(AFSK) to encode and transfer data at a rate of 1200 bits per second, half-duplex at 1200 baud (Mode 2), (or at a "fallback rate" of 600 baud) for the forward data-transmission channel, and an optional 75 baud backward channel.
In some European
countries,(and perhaps elsewhere), V.23 Mode 1 AFSK modulation, (without the backward channel) is used to transmit Caller ID
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
applications where the backward channel was used to sent keyboard data in an asymmetrical full duplex scheme.
communications standard defines a similar modulation scheme.
Modem
A modem is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. The goal is to produce a signal that can be transmitted easily and decoded to reproduce the original digital data...
standard approved by the ITU
Itu
Itu is an old and historic municipality in the state of São Paulo in Brazil. The population in 2009 was 157,384 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language, meaning big waterfall. Itu is linked with the highway numbered the SP-75 and are flowed...
in 1988. It specifies audio frequency-shift keying
Frequency-shift keying
Frequency-shift keying is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. The simplest FSK is binary FSK . BFSK uses a pair of discrete frequencies to transmit binary information. With this scheme, the "1" is called...
(AFSK) to encode and transfer data at a rate of 1200 bits per second, half-duplex at 1200 baud (Mode 2), (or at a "fallback rate" of 600 baud) for the forward data-transmission channel, and an optional 75 baud backward channel.
- V.23 Mode 1 AFSK uses a 1300 Hz tone (FZ) for mark (typically a binary 1) and 2100 Hz (FA) for space (typically a binary 0), and a 1700 Hz center frequency (F0.)
- V.23 Mode 2 AFSK uses a 1300 Hz tone (FZ) for mark (typically a binary 1) and 1700 Hz (FA) for space (typically a binary 0), and a 1500 Hz center frequency (F0.)
- V.23 backward channel AFSK uses a 390 Hz tone (FZ) for mark (typically a binary 1) and a 450 Hz (FA) for space (typically a binary 0).)
In some European
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
countries,(and perhaps elsewhere), V.23 Mode 1 AFSK modulation, (without the backward channel) is used to transmit Caller ID
Caller ID
Caller ID , also called calling line identification or calling number identification or Calling Line Identification Presentation , is a telephone service, available in analog and digital phone systems and most Voice over Internet Protocol applications, that transmits a caller's number to...
information over POTS lines
Plain old telephone service
Plain old telephone service is the voice-grade telephone service that remains the basic form of residential and small business service connection to the telephone network in many parts of the world....
in the public telephone network
Public switched telephone network
The public switched telephone network is the network of the world's public circuit-switched telephone networks. It consists of telephone lines, fiber optic cables, microwave transmission links, cellular networks, communications satellites, and undersea telephone cables, all inter-connected by...
.
The 75 baud backward channel was originally envisioned for use in error correction schemes, but V.23 was also widely used in Videotex
Videotex
Videotex was one of the earliest implementations of an "end-user information system". From the late 1970s to mid-1980s, it was used to deliver information to a user in computer-like format, typically to be displayed on a television.In a strict definition, videotex refers to systems that provide...
applications where the backward channel was used to sent keyboard data in an asymmetrical full duplex scheme.
Related technology
The BELL 202Bell 202 modem
The Bell 202 modem was an early modem developed by Bell System. It specifies audio frequency-shift keying to encode and transfer data at a rate of 1200 bits per second, half-duplex and at a rate of 1800 bits per second full duplex using differential phase-shift keying modulation...
communications standard defines a similar modulation scheme.