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ITU-T Recommendations

​​The main products of ITU-T are Recommendations (ITU-T Recs) - standards defining how telecommunication networks operate and interwork. These can be accessed through the links below. ITU-T Recs have non-mandatory status until they are adopted in national laws. The level of compliance is nonetheless high due to international applicability and the high quality guaranteed by ITU-T's secretariat, and members from the world's foremost information and communication technology (ICT) companies and global administrations.

There are over 4000 Recommendations in force on topics from service definition to network architecture and security, from broadband DSL to Gbit/s optical transmission systems, next-generation networks (NGN) and IP-related issues. All of these topics make part of the fundamental components of today's ICTs.

Membership of ITU-T gives exclusive rights to access working documents of standards under development – tomorrow's ICTs. The vast majority of all Recommendations are available in electronic (PDF) form, free of charge to all, once the final, edited version is published. Texts that are not free of charge include common ITU-T | ISO / IEC texts for which special arrangements exist. Find out more about membership here.

ITU-T Recommendations are available through the Website in tree views, offering multi-criteria search and cross navigation facilities. Each ITU-T Recommendation is cross-linked to the corresponding work programme item, Alternative and Traditional Approval Processes, formal descriptions (more than 1400 freely available), test signals (more than 15 GB of data freely available), supplements, implementer's guides, and IPR statements when applicable.

A to M Series

A : Organization of the work of ITU-T

D : Tariff and accounting principles and international telecommunication/ICT economic and policy issues

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

J : Cable networks and transmission of television, sound programme and other multimedia signals

K : Protection against interference

L : Environment and ICTs, climate change, e-waste, energy efficiency; construction, installation and protection of cables and other elements of outside plant

M : Telecommunication management, including TMN and network maintenance


N to Z Series

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, and associated measurements and tests

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, next-generation networks, Internet of Things and smart cities

Z : Languages and general software aspects for telecommunication systems