The International Telecommunication Union (ITU) was founded on 17.5.1865 in Paris by 20 states and has been a sub-organisation of the United Nations (UN) since 15.10.1947 with its headquarters in Geneva. As of August 1993, its membership numbered 181. The ITU is a worldwide organization in which governments and the private telecommunications sector coordinate the construction and operation of telecommunications networks and services.
The ITU has responsibility for the regulation, standardization, coordination and development of international telecommunications and for the harmonization of national policy interests. The work was previously carried out in the 4 committees Telecommunications Development Bureau (BDT), Comité Consultatif International des Radiocommunications (CCIR), Comité Consultatif International Télégraphique et Téléphonique (CCITT) and International Frequency Registration Board (IFRB). Following a structural reform of the ITU in December 1992, a new constitution came into force on 1 July 1994. The new ITU structure consists of 3 sectors (offices), each headed by a director: Radiocommunication (ITU-R), Telecommunication Standardization (ITU-T) and Telecommunication Development (ITU-D).
The previous CCITT Recommendations are superseded by the ITU Recommendations.
The ITU Recommendations use a letter-number combination for their identification, where the letter describes the scope.
A series: ITU internal organization, procedures, committees.
B-series: Technical terms, definitions, symbols, abbreviations.
D-Series: Costs, tariffs.
E-series: operation of telephone networks, addressing, numbering.
F-series: telegraph services, telematics services, messaging services and directory services.
G-Series: wireline and wireless transmission technology.
H-Series: use of lines for services other than telephony.
I-Series: Integrated Services Digital Networks (ISDN and B-ISDN).
J-Series: Radio and television.
K-Series: Protection against external disturbances, such as interference.
L-Series: Mechanical protection of equipment.
M-Series: Maintenance of audio lines and carrier frequency systems.
N series: Maintenance and quality of broadcasting systems.
O-series: Measurement equipment, procedures and performance.
P-Series: telephone transmission quality, terminal characteristics.
Q-series: telephone signalling, telephone switching.
R-series: teletype equipment.
S-series: terminals for telegraph services.
T-Series: Terminals for telematics services.
U-series: Signalling in telegraph networks.
Y-Series: Global information infrastructure and aspects of the IP protocol.
Z-series: documentation and programming languages.
International Telecommunication Union, Place des Nation, CH-1211 Geneva 20, Switzerland.