science

List of ITU-T V-series recommendations

List of ITU-T V-series recommendations is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand List of ITU-T V-series recommendations rather than just read about it. In short: The ITU-T V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem communication standards and interfaces. Note: the bis and ter suffixes are ITU-T standard designators of successive iterations of a standard (bis and ter are the Latin words for "twice" and "thrice").

Key takeaways

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Reference excerpt

The ITU-T V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem communication standards and interfaces. Note: the bis and ter suffixes are ITU-T standard designators of successive iterations of a standard (bis and ter are the Latin words 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 It has been withdrawn since.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 It has been withdrawn since.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 It has been superseded three times.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/s. Used with the 37-pin ISO 4902 connector ("DC-37"), it is compatible with EIA-422. The 15-pin ISO 4903 connector ("DA-15") is recommended for data network interface. V.17 is an ITU-T recommendation for a fax modem using TCM at 12 and 14.4 kbit/s. V.18 is an ITU-T recommendation for operation and interworking of text telephone devices V.21 is an ITU-T recommendation for full-duplex communication between two analogue dial-up modems using audio frequency-shift keying modulation at 300 baud to carry digital data at 300 bit/s. It is a variant of the original Bell 103 modulation format. V.22 is an ITU-T recommendation for full-duplex communication between two analogue dial-up modems using PSK modulation at 600 baud to carry data at 1200 or 600 bit/s. It is a variant of the Bell 212A modulation format. V.22bis is an ITU-T recommendation extending V.22 with a faster rate using QAM at 600 baud to carry digital data at 2400 or 1200 bit/s. The 1200 bit/s mode is compatible with V.22. V.23 is an ITU-T recommendation for half-duplex communication between two analogue dial-up modems using FSK modulation at up to 600 or 1200 baud to carry digital data at up to 600 or 1200 bit/s respectively. An optional 75 baud reverse channel carries 75 bit/s. V.24 is referenced as RS-232 which also includes V.28. V.25ter see V.250 V.27ter is an ITU-T recommendation for a half-duplex modem, 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, 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 operating as full-duplex on a four-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 of 2,400 baud instead of the 600 baud of the V.22 standards. V.32bis (02/91) is an ITU-T recommendation for a modem, 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.32ter 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 operating as full-duplex on a four-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, allowing up to 28.8 kbit/s bidirectional data transfer using TCM modulation. 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.

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Worked examples

Example 1 — a first encounter with List of ITU-T V-series recommendations

Start with the simplest possible case. Write down what List of ITU-T V-series recommendations claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to List of ITU-T V-series recommendations before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about List of ITU-T V-series recommendations ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of List of ITU-T V-series recommendations

In research: List of ITU-T V-series recommendations appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses List of ITU-T V-series recommendations in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: List of ITU-T V-series recommendations is common in secondary-school and first-year university syllabi. It links to neighbouring topics ITU-T recommendations, Lists of standards, Modems, so understanding it makes those chapters shorter.
In everyday life: Look for List of ITU-T V-series recommendations outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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Frequently asked questions

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Why does List of ITU-T V-series recommendations matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

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Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

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