CCITT, the International Telegraph and Telephone Consultative Committee, is a committee of the International Telecommunications Union (ITU), which is a specialized agency of the United Nations Organization. The ITU, which is located in Geneva, Switzerland, is composed of five subunits: the General Secretariat, the Administrative Council, the International Frequency Registration Board (IFRB), the CCITT, and the CCIR, the International Radio Consultative Committee.

The CCITT's purpose is to recommend standards for communication systems. The goal of these standards is to provide a specification for interconnecting existing telecommunication networks throughout the world and to define a uniform access mechanism to these networks. To date, approximately 2,000 recommendations for standards covering all aspects of telecommunications have been made by CCITT.

About 160 nations participate in the CCITT. They are generally represented by delegations formed by their governmental agencies responsible for telecommunications. For most countries these agencies are their postal, telegraph, and telephone (PTT) administrations. Historically, the United States has participated in CCITT through representatives of AT&T with State Department oversight. In recent years, the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration have become increasingly involved. These official or administration members of CCITT vote on the proposed recommendations.

Telecommunications users and suppliers of communication equipment and services are thus not directly involved in the approval of recommendations. However, they can participate in the process of developing a recommendation through consultation with their national delegation. In addition, four other classes of membership to CCITT are available for nongovernmental participators or observers. Recognized private operating agencies (RPOA) are public or private companies that supply telecommunications services (i.e., AT&T, ITT). CCITT also recognizes some users, manufacturers, and other organizations as scientific and industrial organizations (SIOs). Liaisons are maintained between CCITT and other groups, such as the International Organization for Standardization (ISO), the European Computer Manufacturers Association (ECMA), and the International Telecommunications User's Group (INTUG). Finally, special treaty agencies such as the World Meteorological Organization, which have a vested interest in telecommunications, can participate in CCITT. These groups do not participate directly in the voting on recommendations but contribute greatly to their formulation.

The supreme body of the CCITT is the Plenary Assembly, which is made up of all interested administration members and any RPOA with the approval of an administration member. The Plenary Assembly meets approximately every 4 years and identifies areas of interest and formulates questions that it wishes to study. Study groups are created by the assembly, and questions are assigned to each group for investigation (Table 1).

TABLE 1 CCITT Study Groups

I Telegraph operation and tariff

II Telephone operation and tariff

III General tariff principles

IV Transmission maintenance of international lines, circuits, and chains

V Protection against electromagnetic disturbances

VI Protection and specifications of cable sheaths and poles

VII New networks for data transmission

VIII Telegraph and data terminal equipment; local connecting lines

IX Telegraph transmission quality; specification of equipment and rules for the maintenance of telegraph channels

X Telegraph switching

XI Telephone switching and signaling

XII Telephone transmission performance and local telephone networks

XIII Automatic and semiautomatic telephone networks

XIV Facsimile telegraph transmission and equipment

XV Transmission systems

XVI Telephone circuits

XVII Data transmission

XVIII Digital networks

Much of the work of CCITT is done in study groups. Often working parties are formed from the study group to focus on specific sets of questions. Special rapporteurs may be assigned to coordinate the investigation of specific points of study. The study groups hold international and regional meetings over a study period of 4 years to discuss and attempt to resolve the questions that they have been given. The current study period began in 1985.

At the end of the study period, the recommendations of the study groups are voted on at a Plenary Assembly of the CCITT and, if accepted, are published as official CCITT standard recommendations (Table 2). The multivolume book of recommendations for each study period is given a color designation (i.e., "the yellow book"). Recommendations may be altered or updated by a study group in a subsequent study period.

The official languages of the ITU are French, English, Spanish, Chinese, and Russian, the first three of which are designated as working languages. All CCITT publications are printed in French, with most of them also published in English and Spanish editions.

CCITT recommendations are generally implemented as standards in Europe. The United States and several other countries consider the standards recommendations to have the status of treaties that must be ratified by their respective legislative bodies before adoption. In the United States, existing standards from groups such as the Electronic Industries Association (EIA), The Institute of Electrical and Electronic Engineers (IEEE), and the American National Standards Institute (ANSI) have remained dominant. In newer areas of communication applications, the CCITT recommendations have seen an increasing rate of adoption by American manufacturers of communications equipment and suppliers of communications services.

TABLE 2 CCITT Recommendation Series.

A Organization of the work in CCITT

B Means of expression

D Lease of circuits

E Telephone operations and tariffs

F Telegraph operation and tariffs

G Telephone transmission on metallic lines, radio links, satellite, and radiotelephone systems

H Lines used for the transmission of signals other than telephone signals, such as telegraph, facsimile, data, etc.

I Integrated services digital networks

J Program and television transmission

K Protection against interference

L Protection of cable sheaths and poles

M Maintenance: telephony, telegraphy, and data transmission

N Maintenance: sound program and television transmission

P Quality of telephone transmission

Q Signaling and switching

R Telegraph

S Printing telegraph equipment

T Facsimile

U Telegraph switching

V Data transmission

X Public data networks

Z Software

Of primary interest are the CCITT recommendations for data communications that have been developed by two CCITT study groups (Table 3). Study group VII is responsible for recommending standards for data communication over public data networks. Recommendations developed by this group are given identifiers with the prefix "X" (i.e., X.21, X.25, etc.). These are termed the "X" series recommendations. Study group XVII has the task of recommending standards for data communication over telephone systems. These recommendations have a "V" prefix and are called the "V" series recommendations (i.e.. V.21 and V.24).

TABLE 3 Sample CCITT Recommendations

V.21 300 bits per second duplex modem standardized for use in the general switched telephone network.

V.24 List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-terminating equipment (DCE).

V.54 Loop test devices for modems.

X.21 Interface between DTE and DCE for synchronous operation on public data networks.

X.25 Interface between DTE and DCE for terminals operating in the packet mode on public data networks.

X.75 Terminal and transit call control procedures and data transfer system on international circuits between packet-switched data networks.

The current CCITT work that seems to have attracted the most attention from the telecommunications community is the Integrated Services Digital Network (ISDN) standards development. ISDN's will combine voice, data, and video traffic over a single digital network. These networks will be composed of wire, radio, satellite, and optical links. Other ongoing CCITT work focuses on the development of standards for languages for the description, design, and control of telecommunication networks. Note: CCITT publications may be obtained by contacting

General Secretariat
International Telecommunications Union
Place des Nations
1211 Geneva 20
Switzerland

Bertine, H. V., "Physical Level Interfaces and Protocols," in Data Communications Network Interfacing and Protocols, IEEE, 1981, pp.2-1 - 2-18.

Dickson, G. J., and DeChazal, P. E., "Status of CCITT Description Techniques and Application to Protocol Specification," Proc. IEEE, 71,(12) (December 1983).

Freeman, Roger L., Telecommunication Transmission Handbook, Wiley, New York, 1975.

Lewin, L., ed., Telecommunications: An Interdisciplinary Survey, ArtechHouse, Dedham, MA, 1980.

Levillion, M. E., "Involvement of Users and Manufacturers in the Development of CCITT Packet Switching Recommendations," IEEE Trans. Commun., (February 1984).

Linington, P. F., "Progress in Open Systems Standardization," Interfaces Comput., 2, 205- 220 (1984) .

U.S. Senate Commitee on Commerce, Science, and Transportation, Long-range Goals in International Telecommunications and Information: An outline for United States Policy, U.S. Government Printing Office, Washington, D.C ., 1983.

Yearbook of the United Nations, The United Nations, New York, 1983.