The sector of the ITU that studies technical questions relating to telegraph and telephone communications and establishes international telecommunications standards to ensure the interconnectivity of national networks.The ITU-T previously (1956) was known as the Comité consultatif international télégraphique et téléphonique (CCITT), which translates from French as the International Telegraph and Telephone Consultative Committee. See Table I-5 for ITU-T Series Recommendations. See Appendix A for contact information. See also ITU.

Table I-5: ITU-T Series Recommendations

Series	Description
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
H	Audiovisual and multimedia systems
I	Integrated services digital network (ISDN)
J	Cable networks and transmission of television, sound program and other multimedia signals
K	Protection against interference
L	Construction, installation and protection of cables and other elements of outside plant
M	Telecommunication management, including TMN and network maintenance
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 signaling
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, open system communications and security
Y	Global information infrastructure, Internet protocol aspects and next-generation networks
Z	Languages and general software aspects for telecommunication systems