The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union
International Telecommunication Union
The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...

 (ITU); it coordinates standards for telecommunications.

The standardization
Standardization is the process of developing and implementing technical standards.The goals of standardization can be to help with independence of single suppliers , compatibility, interoperability, safety, repeatability, or quality....

 work of ITU dates back to 1865, with the birth of the International Telegraph Union. It became a United Nations
United Nations
The United Nations is an international organization whose stated aims are facilitating cooperation in international law, international security, economic development, social progress, human rights, and achievement of world peace...

 specialized agency in 1947, and the International Telegraph and Telephone Consultative Committee (CCITT, from ) was created in 1956. It was renamed ITU-T in 1993.

ITU has been an intergovernmental public-private partnership
Public-private partnership
Public–private partnership describes a government service or private business venture which is funded and operated through a partnership of government and one or more private sector companies...

 organization since its inception and now has a membership of 191 countries (Member States) and over 700 public and private sector companies as well as international and regional telecommunication entities, known as Sector Members and Associates, which undertake most of the work of the Sector.

ITU-T has a permanent secretariat, the Telecommunication Standardization Bureau (TSB), based at the ITU HQ in Geneva
Geneva In the national languages of Switzerland the city is known as Genf , Ginevra and Genevra is the second-most-populous city in Switzerland and is the most populous city of Romandie, the French-speaking part of Switzerland...

, Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....

. The elected Director of the Bureau is Malcolm Johnson of the UK. Johnson was elected by the ITU Membership to the directorship for a 4-year term in November 2006 and was reelected for a second term starting January 2011.

Primary function

The ITU-T mission is to ensure the efficient and timely production of standards covering all fields of telecommunications on a worldwide basis, as well as defining tariff and accounting principles for international telecommunication services.

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"), as they become mandatory only when adopted as part of a national law.

Since the ITU-T is part of the ITU, which is a United Nations specialized agency, its standards carry more formal international weight than those of most other standards development organizations that publish technical specifications of a similar form.


Although the ITU itself dates back to 1865, the formal standardization processes are more recent.

Two consultative committees were created by the ITU’s 1925 Paris conference to deal with the complexities of the international telephone services (known as CCIF, as the French acronym) and long-distance telegraphy (CCIT).

In view of the basic similarity of many of the technical problems faced by the CCIF and CCIT, a decision was taken in 1956 to merge them to become the single International Telegraph and Telephone Consultative Committee (CCITT, in the French acronym).

In 1992, the Plenipotentiary Conference (the top policy-making conference of ITU) saw a reform of ITU, giving the Union greater flexibility to adapt to an increasingly complex, interactive and competitive environment. It was at this time that CCITT was renamed the Telecommunication Standardization Sector (ITU-T), as one of three Sectors of the Union alongside the Radiocommunication Sector (ITU-R
The ITU Radiocommunication Sector is one of the three sectors of the International Telecommunication Union and is responsible for radio communication....

) and the Telecommunication Development Sector (ITU-D
The ITU Telecommunication Development] Sector is one of the three sectors of the International Telecommunication Union ; it is responsible for creating policies, regulation and providing training programs and financial strategies in developing countries.Created in 1992, its secretariat is the...


Historically, 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. However, the delays in producing texts, and translating them into other working languages, did not suit the fast pace of change in the telecommunications industry.

"Real time" standardization

The rise of the personal computer
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...

 industry in the early 1980s created a new common practice among both consumers and businesses of adopting "bleeding edge
Bleeding edge
Bleeding edge technology is technology that is so new that it could have a high risk of being unreliable and may incur greater expense in order to use it...

" communications technology even if it was not yet standardized. Thus, standards organization
Standards organization
A standards organization, standards body, standards developing organization , or standards setting organization is any organization whose primary activities are developing, coordinating, promulgating, revising, amending, reissuing, interpreting, or otherwise producing technical standards that are...

s had to put forth standards much faster, or find themselves ratifying de facto standard
De facto standard
A de facto standard is a custom, convention, product, or system that has achieved a dominant position by public acceptance or market forces...

s after the fact.

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. New and updated Recommendations are published on an almost daily basis, and much of the library of over 3,270 Recommendations is now free of charge online. (Specifications jointly maintained by the ITU-T and ISO/IEC are not free.)

ITU-T has moreover tried to facilitate cooperation between the various forums and standard-developing organizations (SDOs). This collaboration is necessary to avoid duplication of work and the consequent risk of conflicting standards in the market place.

In the work of standardization, ITU-T cooperates with other SDOs, e.g., the International Organization for Standardization
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...

 (ISO) and the Internet Engineering Task Force
Internet Engineering Task Force
The Internet Engineering Task Force develops and promotes Internet standards, cooperating closely with the W3C and ISO/IEC standards bodies and dealing in particular with standards of the TCP/IP and Internet protocol suite...


Development of Recommendations

Most of the work of ITU-T is carried out by its Sector Members and Associates, while the Telecommunication Standardization Bureau (TSB) is the executive arm of ITU-T and coordinator for a number of workshops and seminars to progress existing work areas and explore new ones. The events cover a wide array of topics in the field of information and communication technologies (ICT) and attract high-ranking experts as speakers, and attendees from engineers to high-level management from all industry sectors.

The technical work, the development of Recommendations, of ITU-T is managed by Study Groups (SGs). The people involved in these SGs are experts in telecommunications from all over the world. There are currently 13 SGs. Study groups meet face to face according to a calendar issued by the TSB. SGs are augmented by Focus Groups (FGs), an instrument created by ITU-T, providing a way to quickly react to ICT standardization needs and allowing great flexibility in terms of participation and working methods. The key difference between SGs and FGs is that the latter have greater freedom to organize and finance themselves, and to involve non-members in their work. Focus Groups can be created very quickly, are usually short-lived and can choose their own working methods, leadership, financing, and types of deliverables. Recent examples include work on Next Generation Networking
Next Generation Networking
Next-generation network is a broad term used to describe key architectural evolutions in telecommunication core and access networks. The general idea behind the NGN is that one network transports all information and services by encapsulating these into packets, similar to those used on the...

, Internet Protocol Television (IPTV
Internet Protocol television is a system through which television services are delivered using the Internet protocol suite over a packet-switched network such as the Internet, instead of being delivered through traditional terrestrial, satellite signal, and cable television formats.IPTV services...

) and digital identity management.

Approval of Recommendations

The “Alternative Approval Process” (AAP) is a fast-track approval procedure that was developed to allow standards to be brought to market in the timeframe that industry now demands.

This dramatic overhaul of standards-making by streamlining approval procedures was implemented in 2001 and is estimated to have cut the time involved in this critical aspect of the standardization process by 80 to 90 per cent. This means that an average standard which took around four years to approve and publish until the mid nineties, and two years until 1997, can now be approved in an average of two months, or as little as five weeks.

Besides streamlining the underlying procedures involved in the approval process, an important contributory factor to the use of AAP is electronic document handling. Once the approval process has begun the rest of the process can be completed electronically, in the vast majority of cases, with no further physical meetings.

The introduction of AAP also formalizes public/private partnership in the approval process by providing equal opportunities for both Sector Members and Member States in the approval of technical standards.

Once the text of a draft Recommendation prepared by SG experts is considered mature, it is submitted for review to an SG meeting. If agreed by the meeting it is given Consent. This means that the SG has given its consent that the text is sufficiently mature to initiate a final review process leading to approval of the draft Recommendation.

After this Consent has been achieved, TSB announces the start of the AAP procedure by posting the draft text to the ITU-T web site and calling for comments. This gives the opportunity for all members to review the text. This phase, called Last Call, is a four-week period in which comments can be submitted by Member States and Sector Members.

If no comments other than editorial corrections are received, the Recommendation is considered approved since no issues were identified that might need any further work. However, if there are any comments, the SG chairman, in consultation with TSB, sets up a comment resolution process by the concerned experts. The revised text is then posted on the web for an Additional Review period of three weeks.

Similar to the Last Call phase, in Additional Review the Recommendation is considered as approved if no comments are received. If comments are received, it is apparent that there are some issues that still need more work, and the draft text and all comments are sent to the next Study Group meeting for further discussion and possible approval.

Those Recommendations considered as having policy or regulatory implications are approved through what is known as the “Traditional Approval Process” (TAP), which allows a longer period for reflection and commenting by Member States. TAP Recommendations are also translated into the six working languages of ITU (Arabic, Chinese, English, French, Russian and Spanish).

Series and Recommendations

ITU-T Recommendations are the names given to telecommunications and computer protocol specification documents published by ITU-T.

Many of the Recommendations that define OSI are also ISO standards.

Standards for Internet protocols are typically developed in the IETF, and standards for mobile telephone systems are developed in ETSI and other forums.

Series of ITU Recommendations

ITU-T issues Recommendations that have names like X.500
X.500 is a series of computer networking standards covering electronic directory services. The X.500 series was developed by ITU-T, formerly known as CCITT, and first approved in 1988. The directory services were developed in order to support the requirements of X.400 electronic mail exchange and...

, 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.
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
J Cable networks and 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 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 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, 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

G Series Recommendations

Transmission systems and media, digital systems and networks
Specification Range Specification Type
G.8000 - G.8099 Ethernet over Transport aspects
G.8100 - G.8199 MPLS over Transport aspects
G.8200 - G.8299 Quality and availability targets
G.8600 - G.8699 Service Management

Y Series Recommendations

Global Information Infrastructure, Internet Protocol Aspects And Nextgeneration Networks
Specification Range Specification Type
Y.100–Y.199 General
Y.200–Y.299 Services, applications and middleware
Y.300–Y.399 Network aspects
Y.400–Y.499 Interfaces and protocols
Y.500–Y.599 Numbering, addressing and naming
Y.600–Y.699 Operation, administration and maintenance
Y.700–Y.799 Security
Y.800–Y.899 Performances
Y.1000–Y.1099 General
Y.1100–Y.1199 Services and applications
Y.1200–Y.1299 Architecture, access, network capabilities and resource management
Y.1300–Y.1399 Transport
Y.1400–Y.1499 Interworking
Y.1500–Y.1599 Quality of service and network performance
Y.1600–Y.1699 Signalling
Y.1700–Y.1799 Operation, administration and maintenance
Y.1800–Y.1899 Charging
Y.2000–Y.2099 Frameworks and functional architecture models
Y.2100–Y.2199 Quality of Service and performance
Y.2200–Y.2249 Service aspects: Service capabilities and service architecture
Y.2250–Y.2299 Service aspects: Interoperability of services and networks in NGN
Y.2300–Y.2399 Numbering, naming and addressing
Y.2400–Y.2499 Network management
Y.2500–Y.2599 Network control architectures and protocols
Y.2700–Y.2799 Security
Y.2800–Y.2899 Generalized mobility

International Telecommunication Regulations (ITRs)

In addition to the ITU-T Recommendations, which have non-mandatory status until they are adopted in national laws, ITU-T is also the custodian of a binding international treaty, the International Telecommunication Regulations. The ITRs go back to the earliest days of the ITU when there were two separate treaties, dealing with telegraph and telephone. The ITRs were adopted, as a single treaty, at the World Administrative Telegraphy and Telephone Conference held in Melbourne, 1988 (WATTC-88).

In line with the current Constitution and Convention of ITU, the ITRs can be amended through a World Conference on International Telecommunications (WCIT), and the next is scheduled for 2012. Before then a process of review of the ITRs, which began in 1998, will continue.

The ITRs comprise ten articles which deal, inter alia, with the definition of international telecommunication services, cooperation between countries and national administrations, safety of life and priority of telecommunications and charging and accounting principles. The adoption of the ITRs in 1988 is often taken as the start of the wider liberalization process in international telecommunications, though a few countries, including United States and United Kingdom, had made steps to liberalize their markets before 1988.

Key standards published by ITU

  • ASN.1 (Abstract Syntax Notation One)
  • Coding of audio G.711
    G.711 is an ITU-T standard for audio companding. It is primarily used in telephony. The standard was released for usage in 1972. Its formal name is Pulse code modulation of voice frequencies. It is required standard in many technologies, for example in H.320 and H.323 specifications. It can also...

     and G.72x series
  • Coding of still images JPEG
    In computing, JPEG . The degree of compression can be adjusted, allowing a selectable tradeoff between storage size and image quality. JPEG typically achieves 10:1 compression with little perceptible loss in image quality....

     T.80 and JPEG 2000
    JPEG 2000
    JPEG 2000 is an image compression standard and coding system. It was created by the Joint Photographic Experts Group committee in 2000 with the intention of superseding their original discrete cosine transform-based JPEG standard with a newly designed, wavelet-based method...

     T.800 series
  • Coding of video coding H.262
    H.262 or MPEG-2 Part 2 is a digital video compression and encoding standard developed and maintained jointly by ITU-T Video Coding Experts Group and ISO/IEC Moving Picture Experts Group . It is the second part of the ISO/IEC MPEG-2 standard...

    /MPEG2-Video and H.264/MPEG-4 AVC
  • Construction, installation and protection of cables and other elements of outside plant, L-series
  • Data communication over the telephone network, V-series
  • Fax
    Fax , sometimes called telecopying, is the telephonic transmission of scanned printed material , normally to a telephone number connected to a printer or other output device...

     standards T.2 – T.4, T.30, T.37, T.38
    T.38 is an ITU recommendation for allowing transmission of fax over IP networks in real time.- History :The T.38 fax relay standard was devised in 1998 as a way to permit faxes to be transported across IP networks between existing Group 3 fax terminals. T.4 and related fax standards were published...

  • is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...

     (Next generation wired home networking over powerlines, phonelines and coaxial cable)
  • H.323
    H.323 is a recommendation from the ITU Telecommunication Standardization Sector that defines the protocols to provide audio-visual communication sessions on any packet network...

     family of standards for multimedia and VoIP
  • Interconnection rate harmonization, D-series
  • International Emergency Preference Scheme E.106
  • IMSI codes used in SIM
    Subscriber Identity Module
    A subscriber identity module or subscriber identification module is an integrated circuit that securely stores the International Mobile Subscriber Identity and the related key used to identify and authenticate subscriber on mobile telephony devices .A SIM is held on a removable SIM card, which...

     cards E.212
  • ISDN and PSTN/3G
    3G or 3rd generation mobile telecommunications is a generation of standards for mobile phones and mobile telecommunication services fulfilling the International Mobile Telecommunications-2000 specifications by the International Telecommunication Union...

     videoconferencing systems, H.320
    H.320 is an umbrella recommendation by the ITU-T for running Multimedia over ISDN based networks. The main protocols in this suite are H.221, H.230, H.242, audio codecs such as G.711, and video codecs such as H.261 and H.263....

     and H.324
    H.324 is an ITU-T recommendation for voice, video and data transmission over regular analog phone lines. It uses a regular 33,600 bit/s modem for transmission, the H.263 codec for video encoding and G.723.1 for audio....

  • ISDN (Integrated Services Digital Network) Q.931
    ITU-T Recommendation Q.931 is ISDN's connection control protocol, roughly comparable to TCP in the Internet Protocol stack. Q.931 doesn't provide flow control or perform retransmission, since the underlying layers are assumed to be reliable and the circuit-oriented nature of ISDN allocates...

  • Open Systems Interconnection
    Open Systems Interconnection
    Open Systems Interconnection is an effort to standardize networking that was started in 1977 by the International Organization for Standardization , along with the ITU-T.-History:...

  • Optical Transport Network
    Optical Transport Network
    ITU-T defines an Optical Transport Network as a set of Optical Network Elements connected by optical fibre links, able to provide functionality of transport, multiplexing, switching, management, supervision and survivability of optical channels carrying client signals...

     (OTN) G.709
    ITU-T Recommendation G.709 "Interfaces for the Optical Transport Network " describes a means of communicating data over an optical network...

    , G.798
  • Passive optical network
    Passive optical network
    A passive optical network is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 16-128. A PON consists of an optical line terminal at the service provider's central...

    s (PON) G.983
    ITU-T Recommendation G.983 is a family of recommendations that defines Broadband Passive Optical Network for telecommunications Access networks. It originally comprised ten recommendations, G.983.1 through G.983.10, but recommendations .6–.10 were withdrawn when their content was...

    , G.984
    ITU-T Recommendation G.984 is a family of recommendations that defines gigabit passive optical networks for telecommunications access networks...

    , G.987
    ITU-T Recommendation G.987 is a family of recommendations that defines 10 gigabit passive optical networks for telecommunications access networks...

  • Public Key Infrastructure
    Public key infrastructure
    Public Key Infrastructure is a set of hardware, software, people, policies, and procedures needed to create, manage, distribute, use, store, and revoke digital certificates. In cryptography, a PKI is an arrangement that binds public keys with respective user identities by means of a certificate...

     (PKI) X.509
    In cryptography, X.509 is an ITU-T standard for a public key infrastructure and Privilege Management Infrastructure . X.509 specifies, amongst other things, standard formats for public key certificates, certificate revocation lists, attribute certificates, and a certification path validation...

  • Public telecommunication numbering plan, E.164
    E.164 is an ITU-T recommendation that defines the international public telecommunication numbering plan used in the PSTN and some other data networks. It also defines the format of telephone numbers. E.164 numbers can have a maximum of fifteen digits and are usually written with a + prefix...

  • Security framework X.805
  • Signalling System 7
    Signalling System 7
    Signalling System No. 7 is a set of telephony signaling protocols which are used to set up most of the world's public switched telephone network telephone calls. The main purpose is to set up and tear down telephone calls...

     Q.7xx series
  • Standards relating to Quality of Service
    Quality of service
    The quality of service refers to several related aspects of telephony and computer networks that allow the transport of traffic with special requirements...

  • Specification and Description Language
    Specification and Description Language
    Specification and Description Language is a specification language targeted at the unambiguous specification and description of the behaviour of reactive and distributed systems.- Overview :It is defined by the ITU-T...

  • Synchronous Digital Hierarchy (SDH) G.707 – G.803
  • Wavelength-division multiplexing
    Wavelength-division multiplexing
    In fiber-optic communications, wavelength-division multiplexing is a technology which multiplexes a number of optical carrier signals onto a single optical fiber by using different wavelengths of laser light...

  • X.25
    X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, and leased lines, Plain old telephone service connections or ISDN connections as physical links...

  • (x)DSL (Digital Subscriber Line) series of standards for broadband telecoms

Hot topics

  • ITU-T is committed to “bridging the standardization gap” – disparities in the ability of developing countries, relative to developed ones, to access, implement, contribute to and influence international ICT standards.
  • The ICT Security Standards Roadmap has been developed to assist in the development of security standards by bringing together information about existing standards and current standards work in key standards development organizations.
  • The Next Generation Networks (NGN) concept takes into consideration new realities in the telecommunication industry characterized by factors such as; the need to converge and optimize the operating networks and the extraordinary expansion of digital traffic (i.e., increasing demand for new multimedia services, mobility, etc.).

See also

  • Global Standards Collaboration
    Global Standards Collaboration
    The "Global Standards Collaboration" started life as The "Inter-regional Telecommunications Standards conference in 1990. This was an initiative of the T1 Committee of the United States who invited the other founding partner organizations ITU-T, ETSI and the Japanese TTC to the first ISC Meeting...

  • International Telecommunication Union
    International Telecommunication Union
    The International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...

ITU-R recommendations
ITU-T recommendations
  • World Summit on the Information Society
    World Summit on the Information Society
    The World Summit on the Information Society was a pair of United Nations-sponsored conferences about information, communication and, in broad terms, the information society that took place in 2003 in Geneva and in 2005 in Tunis...

External links

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