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ITU Telecommunication Standardization Sector

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The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland. Prior to 1992, it was known as the International Telegraph and Telephone Consultative Committee (CCITT, from the French name "Comité consultatif international téléphonique et télégraphique").

Contents

Primary function

The international standards that are produced by the ITU-T are referred to as "Recommendations" (with the word ordinarily capitalized to distinguish its meaning from the ordinary sense of the word "recommendation"). Since the ITU-T is part of the ITU, which is a United Nations Organization (UNO), its standards carry more formal international recognition than those of most other organizations that publish technical specifications of a similar form.

The sector divides its work into categories that are each identified by a single letter, referred to as the "series" (see below), and Recommendations are numbered within each series, for example "V.90".

History

Historically from 1960 until the formation of ITU-T in 1992, the Recommendations of the CCITT were presented to four-yearly "plenary assemblies" for endorsement, and the full set of Recommendations were published after each plenary assembly, in a set of volumes titled collectively for the colour of their covers. For example the publication after the 1980 plenary session was the Yellow Book while that after 1984 was the Red Book and that after 1988 was the Blue Book. These publications were divided into "fascicles" of several hundred pages that could be bought separately. The four-year approval cycle made the CCITT a rather slow and deliberate organization.

ITU reorganization 1970s-1990s

The rise of the personal computer industry in the early 1980s created a new common practice among both consumers and businesses of adopting "bleeding edge" communications technology even if it was not yet standardized. Thus, standards organizations had to put forth standards much faster, or find themselves ratifying de facto standards after the fact. Unfortunately, like the International Organization for Standardization (ISO), CCITT was slow to adapt.

In some cases, a hopeless hodgepodge of proprietary standards resulted, with no clear winner; this was and still is the case with color fax technology. Another phenomenon was that the general public sought standards from organizations which it perceived as more responsive or inclusive; these included informal non-governmental organizations like the Internet Engineering Task Force (IETF) or private consortia like the World Wide Web Consortium (W3C).

ITU's \"real time\" standardization: 2000-Present

In response to the mess that previous ITU practices had created, the ITU-T now operates under much more streamlined processes. The time between an initial proposal of a draft document by a member company and the final approval of a full-status ITU-T Recommendation can now be as short as a few months (or less in some cases). This makes the standardization approval process in the ITU-T much more responsive to the needs of rapid technology development than in the ITU's historical past, but also means that the standards organization's classical functions of quality control and public review have far less time to be effective.

Changes in ITU-T compliance practices

A standard that has been amended can (if desired) retain its designation so that, for example, in the mid-1980s, terminal equipment for connection to an X.25 (packet switched) network might need alternative modes of operation depending on whether the network implemented the 1980 (Yellow Book) or the 1984 (Red Book) version of the standard. However, it is now more common for older versions of a standard to simply be marked as "superseded" when a standard is revised, and features of prior versions are ordinarily kept unchanged within the specification as new enhancements are added in new versions. 
A standard can be developed that extends or is complementary to an existing one rather than replacing it. Such a standard is sometimes designated by the suffix "bis" or "ter" added to the base standard name, for example "V.26bis" and "V.26ter".



Series and Recommendations


ITU-T issues Recommendations that have names like X.500, where X is the series and 500 is an identifying number. When a Recommendation is updated, it will (mostly) keep the same number, so the year of issue may be necessary to identify a specific version of a recommendation.
The term "X.500" is used both to refer to the specific X.500 recommendation, and to the entire family of recommendations named X.5xx, where the specific X.500 recommendation forms the introduction and overview to the set.


See .


Significant ITU-T series and Recommendations are:

A - Organization of the work of ITU-T


B - Means of expression: definitions, symbols, classification


C - General telecommunication statistics


D - General tariff principles


E - Overall network operation, telephone service, service operation and human factors


F - Non-telephone telecommunication services


G - Transmission systems and media, digital systems and networks


Often just called the G-standards.





H - Audiovisual and multimedia systems



I - Integrated services digital network (

J - Transmission of television, sound programme and other multimedia signals


K - Protection against interference


L - Construction, installation and protection of cables and other elements of outside plant


M - 

N - Maintenance: international sound programme and television transmission circuits


O - Specifications of measuring equipment


P - Telephone transmission quality, telephone installations, local line networks


Q - Switching and signalling



R - Telegraph transmission


S - Telegraph services terminal equipment


T - Terminals for telematic services



U - Telegraph switching


V - Data communication over the telephone network





X - Data networks and open system communication



Y - Global information infrastructure and Internet protocol aspects


Z - Languages and general software aspects for telecommunication systems





See also





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