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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 Co ...
V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved
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 modulating one or more c ...
communication standards and interfaces. ''Note:'' the '' bis'' and ''
ter Ter or TER may refer to: Places * River Ter, in Essex, England * Ter (river), in Catalonia * Ter (department), a region in France * Torre (river), (Slovene: ''Ter''), a river in Italy * Ter, Ljubno, a settlement in the Municipality of Ljubno o ...
'' suffixes are ITU-T standard designators of successive iterations of a standard (''bis'' and ''ter'' are derived from the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
for "twice" and "thrice").


General standards

''Applies to V.1–V.9'' *V.1 is an ITU-T recommendation, entitled ''Equivalence between binary notation symbols and the significant conditions of a two-condition code.'' *V.2 is an ITU-T recommendation, approved in November 1988, titled ''Power levels for data transmission over telephone lines.'' *V.4 is an ITU-T recommendation, approved in November 1988, titled ''General structure of signals of International Alphabet No. 5 code for character oriented data transmission over public telephone networks.'' *V.5 was an ITU-T recommendation, approved in November 1988, titled ''Standardization of data signalling rates for synchronous data transmission in the general switched telephone network.'' It has been withdrawn since. *V.6 was an ITU-T recommendation, approved in November 1988, titled ''Standardization of data signalling rates for synchronous data transmission on leased telephone-type circuits.'' It has been withdrawn since. *V.7 is an ITU-T recommendation, approved in November 1988, titled ''Definitions of terms concerning data communication over the telephone network.'' *V.8 is an ITU-T recommendation, first approved in September 1994, titled ''Procedures for starting sessions of data transmission over the public switched telephone network.'' It has been superseded three times. The current version was approved in November 2000. *V.8bis is an ITU-T recommendation, first approved in August 1996, titled ''Procedures for the identification and selection of common modes of operation between data circuit-terminating equipments (DCEs) and between data terminal equipments (DTEs) over the public switched telephone network and on leased point-to-point telephone-type circuits.'' It has been superseded twice. The current version was approved in November 2000.


Interfaces and voiceband modems

''Applies to V.10–V.34'' *V.10 is an ITU-T recommendation, first agreed in 1976, for unbalanced electrical circuits for data communication at up to 100 kbit/s. It can interwork with V.28, provided it is not exposed to signals greater than 12 volts. Used with the 37-pin ISO 4902 connector, it is compatible with EIA RS-423. *V.11 is an ITU-T recommendation, first agreed in 1976, for balanced electrical circuits for data communication at up to 10
Mbit The megabit is a multiple of the unit bit for digital information. The prefix mega (symbol M) is defined in the International System of Units (SI) as a multiplier of 106 (1 million), and therefore :1 megabit = = = 1000 kilobits. The megabit ...
/s. Used with the 37-pin ISO 4902 connector (" DC-37"), it is compatible with
EIA-422 RS-422, also known as TIA/EIA-422, is a technical standard originated by the Electronic Industries Alliance that specifies electrical characteristics of a digital signaling circuit. It was meant to be the foundation of a suite of standards that ...
. The 15-pin ISO 4903 connector ("
DA-15 The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems. Description, no ...
") is recommended for data network interface. *V.17 is an ITU-T recommendation for a fax modem using TCM
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...
at 12 and 14.4 kbit/s. *V.21 is an ITU-T recommendation for
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 ...
communication between two analogue dial-up
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 modulating one or more c ...
s using
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 ...
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...
at 300
baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...
to carry
digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals ** Digital camera, which captures and stores digital ...
data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...
at 300
bit/s 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 ...
. It is a variant of the original
Bell 103 The Bell 103 modem or Bell 103 dataset was the second commercial modem for computers, released by AT&T Corporation in 1962. It allowed digital data to be transmitted over regular unconditioned telephone lines at a speed of 300 bits per second. I ...
modulation format. *V.22 is an ITU-T recommendation for
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 ...
communication between two analogue dial-up
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 modulating one or more c ...
s using PSK
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...
at 600
baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...
to carry data at 1200 or 600
bit/s 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 ...
. It is a variant of the
Bell 212A The Bell 212A modulation scheme defined a standard method of transmitting full-duplex asynchronous serial data at 1.2 kbit/s over analogue transmission lines. The equivalent, but incompatible ITU-T standard is V.22. Device The Bell 212 Dataset i ...
modulation format. *V.22bis is an ITU-T recommendation extending V.22 with a faster rate using QAM at 600
baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...
to carry
digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals ** Digital camera, which captures and stores digital ...
data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...
at 2400 or 1200
bit/s 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 ...
. The 1200 bit/s mode is compatible with V.22. *
V.23 ''V.'' is the debut novel of Thomas Pynchon, published in 1963. It describes the exploits of a discharged U.S. Navy sailor named Benny Profane, his reconnection in New York with a group of pseudo- bohemian artists and hangers-on known as the Wh ...
is an ITU-T recommendation for half-duplex communication between two analogue dial-up
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 modulating one or more c ...
s using FSK
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...
at up to 600 or 1200
baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...
to carry
digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals ** Digital camera, which captures and stores digital ...
data In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpret ...
at up to 600 or 1200
bit/s 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 ...
respectively. An optional 75 baud reverse channel carries 75 bit/s. *V.24 is referenced as
RS-232 In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' ('' data terminal equipment'') suc ...
which also includes V.28. *V.250 (also known as V.25ter) is extended data modems ITU-T recommendation . *V.27ter is an ITU-T recommendation for a half-duplex
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 modulating one or more c ...
, allowing 2400 and 4800 bit/s ( PSK modulation). *V.28 is an ITU-T recommendation defining the electrical characteristics for unbalanced double-current interchange circuits. *V.29 is an ITU-T recommendation for a
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 modulating one or more c ...
, allowing 4.8 kbit/s, 7.2 kbit/s and 9.6 kbit/s transfer modes ( PSK and QAM modulations). *V.32 (11/88) is an ITU-T recommendation for a
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 modulating one or more c ...
operating as
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 ...
on a 4-wire circuit, or half-duplex on a two-wire circuit, allowing bidirectional data transfer at either 9.6 kbit/s or 4.8 kbit/s at a
symbol rate In a digitally modulated signal or a line code, symbol rate, modulation rate or baud rate is the number of symbol changes, waveform changes, or signaling events across the transmission medium per unit of time. The symbol rate is measured in ' ...
of 2,400
baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...
instead of the 600
baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulat ...
of the V.22 standards. **V.32bis (02/91) is an ITU-T recommendation for a
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 modulating one or more c ...
, allowing up to 14.4 kbit/s bidirectional data transfer. Other additional defined data transfer rates are 12.0 kbit/s, 9.6 kbit/s, 7.2 kbit/s, and 4.8 kbit/s. The standard was extended by several modem manufacturers to allow bidirectional data transfer rates of 19.2 kbit/s, but never ratified as a V.32''ter'' standard. These non-ITU-T standard modems were often referred to as 'V.32terbo' modems. *V.33 is an ITU-T recommendation for a
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 modulating one or more c ...
operating as
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 ...
on a 4-wire point-to-point leased line allowing bidirectional data transfer at either 14.4 kbit/s. *V.34 (09/94) is an ITU-T recommendation (superseded) for a
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 modulating one or more c ...
, allowing up to 28.8 kbit/s bidirectional data transfer using TCM
modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...
. Other additional defined data transfer rates are 24.0 kbit/s and 19.2 kbit/s as well as all the permitted V.32 and V.32bis rates. Additionally, V.34 modems employ shell mapping as shaping code to reduce the transmit power. **V.34 (10/96) is an updated ITU-T recommendation for a modem, building on the V.34 standard but allowing up to 33.6 kbit/s bidirectional data transfer. Other additional defined data transfer rates are 31.2 kbit/s, as well as all the permitted V.34 rates. Modems implementing this standard were often marketed under the moniker V.34+. **V.34 (02/98) commonly rendered as V.34bis, is a further update to V.34 which corrected some errata in the original 1996 document.


Ad hoc standards

In order to gain first-mover advantage, many modem companies introduced models based on upcoming V-series standards before they reached final ratification. In other cases, companies introduced non-standard systems but gave them ITU-like names. *V.32terbo, or V.32ter for short, was a 19.2 kbit/s standard introduced by AT&T Paradyne. It was based on V.32bis and did little other than increase the data rate. V.32ter is compatible with V.32bis at speeds of 14.4 kbit/s and lower, but it is not compatible with V.34 at 19.2. *V.FC, short for V.Fast Class and sometimes referred to as V.FAST, was developed by
Hayes Hayes may refer to: * Hayes (surname), including a list of people with the name ** Rutherford B. Hayes, 19th president of the United States * Hayes (given name) Businesses * Hayes Brake, an American designer and manufacturer of disc brakes * Hay ...
and Rockwell to introduce a 28.8 kbit/s standard while the V.34 efforts dragged on. V.FC was not compatible with V.34, although most V.34 modems could support V.FC, notably, those using Rockwell chipsets. *K56flex was developed by Rockwell and Lucent while the V.90 standards were underway. Compatibility problems between the two companies' implementations were a concern, and the standard quickly disappeared. *X2 was USRobotics' answer to K56flex, and likewise disappeared rapidly with the introduction of V.90.


Wideband modems

''Applies to V.35–V.39'' *V.35 is an ITU-T standard located on layer 1 on the
OSI model The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...
. Max speed is 2 Mbit/s. Withdrawn ITU-T recommendation for 48 kbit/s data transmission over wideband circuits. The physical and electrical characteristics of this interface are now specified in ITU-T recommendation V.11. *V.36 is an ITU-T standard located on layer 2 on the
OSI model The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications ...
called Modems For Synchronous Data Transmission Using 60–108 kHz Group Band Circuits.


Error control and data compression

''Applies to V.40–V.49'' *V.41 is a code-independent error control system. Defines the
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 Co ...
standard CRC-16 polynomial as x16 + x12 + x5 + 1 *V.42 is an error correction protocol. Its function is to allow the receiver to immediately request re-transmission of any lost data packets. However, it does not guarantee how quickly the error-free data will be delivered to the receiving end. V.42 is generally included in dialup modems. Also defines the ITU-T standard CRC-32 polynomial as x32+x26+x23+x22+x16+x12+x11+x10+x8+x7+x5+x4+x2+x+1, and includes the LAPM framing protocol. *V.42bis, also an adaptive data compression standard, is based on the Lempel Ziv dynamic dictionary approach, and may go to "transparent mode," in which data is transmitted uncompressed. The specific algorithm is " BTLZ" (British Telecom Lempel Ziv), which was developed by Alan Clark (then with BT). *V.44 is based on LZJH (Lempel-Ziv-Jeff-Heath) adaptive data compression developed by Hughes Electronics for its DirecPC satellite Internet, and incorporated into the v.92 dial-up modem standard. V.44 offers somewhat better compression performance for certain types of data than the V.42bis standard, on average allowing 15% greater throughput. For instance, a 53.3 kbit/s connection with V.44 can transmit up to 53.3×6 = 320 kbit/s using pure text. In reality, the overall data rate rarely exceeds 3:1 compression (~150 kbit/s). The compression tends to get better and worse over time due to noise on the line, or due to the transfer of already-compressed files (ZIP files, JPEG images, MP3 audio, MPEG video). At some points the modem will be sending compressed files at 53 kbit/s, uncompressed files at 160 kbit/s, and pure text at 320 kbit/s, or any value in between.


Simultaneous transmission of data and other signals

''Applies to V.60–V.99'' * V.61 Analog Simultaneous Voice and Data (ASVD) *V.70 Digital Simultaneous Voice and Data (DSVD) *V.80:
videoconferencing Videotelephony, also known as videoconferencing and video teleconferencing, is the two-way or multipoint reception and transmission of audio signal, audio and video signals by people in different locations for Real-time, real time communication. ...
. It is generally compatibilized with
H.324 H.324 is an ITU-T recommendation for voice, video and data transmission over regular analog phone lines. It uses a regular 33,600 bit/s modem for transmission, the H.263 codec for video encoding and G.723.1 for audio. H.324 standard is formal ...
standard point-to-point video telephony over regular phone lines. *V.90 is an ITU-T recommendation for a
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 modulating one or more c ...
, allowing 56 kbit/s digital download and 33.6 kbit/s analog upload. It replaced two vendor standards ( K56flex and X2) and was designed to allow modems from both prior standards to be flash upgraded to support it. It is also known as ''V.Last'' as it was anticipated to be the last standard for modems operating near the channel capacity of POTS lines to be developed. V.90 is generally used in concert with the V.42bis compression standard. *V.91: ''A digital modem operating at data signalling rates of up to 64 000 bit/s for use on a 4-wire circuit switched connection and on leased point-to-point 4-wire digital circuits'', published in 1999 *
V.92 V.92 is an ITU-T recommendation, titled ''Enhancements to Recommendation V.90'', that establishes a modem standard allowing near 56 kb/s download and 48 kb/s upload rates. With V.92 PCM is used for both the upstream and downstream connections; pre ...
is an
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 Co ...
recommendation, titled ''Enhancements to Recommendation V.90'', that establishes a
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 modulating one or more c ...
standard allowing 56 kbit/s download, 48 kbit/s upload rates, and the new V.44 compression method. It is intended to succeed the V.90 standards. With V.92,
PCM Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the am ...
is used for both the upstream and downstream connections; previously 56K modems only used PCM for downstream data.


Interworking with other networks

''Applies to V.100–V.199'' *V.110 is an ITU-T recommendation for using terminal adaptor functions for the connection of terminals having interfaces conforming to V-series to the ISDN. *V.120 is an alternative to V.110 based on the LAPD protocol. *V.150.1 is an ITU-T recommendation for using a
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 modulating one or more c ...
over IP networks. *V.152 is an ITU-T recommendation for using Voice-Band Data over IP Networks.


Interface layer specifications for data communication

''Applies to V.200–V.249'' *V.230 is an ITU-T recommendation, approved in November 1988, titled ''General data communications interface layer 1 specification.''


Digital circuit modems

''Applies to V.400–V.499'' *V.300 is an ITU-T recommendation, first approved in January 1997, titled ''A 128 (144) kbit/s data circuit-terminating equipment standardized for use on digital point-to-point leased circuits''.


See also

*
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 Co ...
* 56 kbit/s modem * Microcom Networking Protocols (MNP1 to 10) *
List of device bandwidths This is a list of interface bit rates, is a measure of information transfer rates, or digital bandwidth capacity, at which digital interfaces in a computer or network can communicate over various kinds of buses and channels. The distinction can ...


References


External links


ITU-T Recommendations: V Series
nbsp;– Includes pinouts and history
V.44 FAQ
* ttp://3amSystems.com/wireline/hmo.htm Basic handshakes & modulationsnbsp;– V.22, V.22bis & V.32 handshakes {{Modem standards ITU-T V-series V-Series ITU-T V-series