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The '''ITU Telecommunication [[Standardization]] Sector''' ('''ITU-T''') coordinates standards for telecommunications on behalf of the [[International Telecommunication Union]] (ITU) and is based in [[Geneva]], [[Switzerland]]. Prior to [[1992]], it was known as the '''International Telephone and Telegraph Consultative Committee''' ('''CCITT''', from the French name "'''Comité consultatif international téléphonique et télégraphique'''").
The '''ITU Telecommunication [[Standardization]] Sector''' ('''ITU-T''') coordinates ''standards for telecommunications'' on behalf of the [[International Telecommunication Union]] (ITU) and is based in [[Geneva]], [[Switzerland]].


The standardization work of ITU dates back to 1865, with the birth of the International Telegraph Union. It became a [[United Nations]] specialized agency in 1947, and the International Telegraph and Telephone Consultative Committee (CCITT), (from the French name "Comité Consultatif International Téléphonique et Télégraphique") was created in 1956. It was renamed ITU-T in 1993.<ref>http://www.itu.int/net/about/landmarks.aspx</ref>
=== Primary function ===
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"). Since the ITU-T is part of the ITU, which is a [[United Nations]] Organization (UNO), its standards carry more formal international recognition than those of most other organizations that publish technical specifications of a similar form.


ITU has been an intergovernmental [[public-private partnership]] 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.<ref>http://www.itu.int/net/about/index.aspx</ref>
The sector divides its work into categories that are each identified by a single letter, referred to as the "series" (see below), and Recommendations are numbered within each series, for example "V.90".


=== History ===
== 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.<ref>http://www.itu.int/ITU-T/info/index.html</ref>
Historically from 1960 until the formation of ITU-T in 1992, 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, in a set of volumes titled collectively for the colour of their covers. For example the publication after the 1980 plenary session was the ''Yellow Book'' while that after 1984 was the ''[[Red Book (ITU-T)]]'' and that after 1988 was the ''Blue Book''. These publications were divided into "fascicles" of several hundred pages that could be bought separately. The four-year approval cycle made the CCITT a rather slow and deliberate organization.


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 only become mandatory when adopted as part of a national law.
=== ITU reorganization 1970s–1990s ===
The rise of the [[personal computer]] industry in the early 1980s created a new common practice among both consumers and businesses of adopting "[[bleeding edge]]" communications technology even if it was not yet standardized. Thus, standards organizations had to put forth standards much faster, or find themselves ratifying ''de facto'' standards after the fact. Unfortunately, like the [[International Organization for Standardization]] (ISO), CCITT was slow to adapt.


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.<ref>http://www.apdip.net/publications/iespprimers/eprimer-igov.pdf (p13)</ref>
=== ITU's "real time" standardization: 2000–present ===
In response to the mess that previous ITU practices had created, 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, but also means that the standards organization's classical functions of quality control and public review have far less time to be effective.


== History ==
=== Changes in ITU-T compliance practices ===
Although the ITU itself dates back to 1865<ref>http://www.itu.int/net/about/history.aspx</ref>, the formal standardization processes are more recent.
A standard that has been amended can (if desired) retain its designation so that, for example, in the mid-1980s, terminal equipment for connection to an [[X.25]] (packet switched) network might need alternative modes of operation depending on whether the network implemented the 1980 (''Yellow Book'') or the 1984 (''Red Book'') version of the standard. However, it is now more common for older versions of a standard to simply be marked as "superseded" when a standard is revised, and features of prior versions are ordinarily kept unchanged within the specification as new enhancements are added in new versions.
A standard can be developed that extends or is complementary to an existing one rather than replacing it. Such a standard is sometimes designated by the suffix "bis" or "ter" added to the base standard name, for example "V.26bis" and "V.26ter".


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).<ref>http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p8)</ref>
==Series and Recommendations==


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).<ref>http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p8)</ref>
ITU-T issues Recommendations that have names like [[X.500]], 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.


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]]) and the Telecommunication Development Sector ([[ITU-D]]).<ref>http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p14)</ref>
See [[:Category:ITU-T recommendations]].


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.<ref>http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf</ref>
Significant ITU-T series and Recommendations are:
===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===
*[[E.123]] Notation for national and international telephone numbers
*[[E.163]] Numbering plan for the international telephone service
*[[E.164]] The international public telecommunication numbering plan
** Supplement 2 - Number Portability
===F - Non-telephone telecommunication services===
===G - Transmission systems and media, digital systems and networks===


== "Real time" standardization ==
Often just called the '''G-standards'''.
The rise of the [[personal computer]] industry in the early 1980s created a new common practice among both consumers and businesses of adopting "[[bleeding edge]]" communications technology even if it was not yet standardized. Thus, standards organizations had to put forth standards much faster, or find themselves ratifying [[de facto standard]]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.<ref>http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p16)</ref> New and updated Recommendations are published on an almost daily basis, and the entire library of over 3’270 Recommendations is now free of charge online.
*[[G.165]] Echo cancellers
*[[G.651]] Characteristics of a 50/125 µm multimode graded index optical fibre cable
*[[G.652]] Characteristics of a single-mode optical fibre and cable
*[[G.655]] Characteristics of a Bending Loss Insensitive Single Mode Optical Fibre and Cable for the Access Network
*[[G.703]] Physical/electrical characteristics of hierarchical digital interfaces
*[[G.704]] Synchronous frame structures used at 1544, 6312, 2048, 8448 and 44 736 kbit/s hierarchical levels
*[[G.707]] Network node interface for the [[Synchronous Digital Hierarchy]] ([[Synchronous Digital Hierarchy|SDH]])
*[[G.709]] Interfaces for the [[Optical Transport Network]] ([[Optical Transport Network|OTN]])
*[[G.711]] Audio compression ([[mu-law algorithm|mu-law]] and [[a-law algorithm|a-law]])
*[[G.721]] Audio compression [[ADPCM]] (superseded by G.726)
*[[G.722]] Audio compression (wideband)
*[[G.722.1]] Audio compression (wideband, lower bit rates)
*[[G.722.2]] Speech compression [[AMR-WB]] (wideband, lower bit rates)
*[[G.723.1]] Speech compression [[CELP]]
*[[G.726]] Audio compression ADPCM
*[[G.727]] Audio compression ADPCM (variant of G.726)
*[[G.728]] Speech compression [[LD-CELP]]
*[[G.729]] Speech compression [[ACELP]]
*[[ITU-T Recommendation G.783|G.783]] Characteristics of synchronous digital hierarchy ([[Synchronous Digital Hierarchy|SDH]]) equipment functional blocks
*[[ITU-T Recommendation G.798|G.798]] Characteristics of [[OTN|Optical Transport Network]] hierarchy equipment functional blocks
*[[G.805]] Generic functional architecture of transport networks
*[[ITU-T Recommendation G.806|G.806]] Characteristics of transport equipment – Description methodology and generic functionality
*G.982 Optical access networks to support services up to the ISDN primary rate or equivalent bit rates
*[[G.983]] Broadband optical access systems based on Passive Optical Networks ([[Passive Optical Network|PON]])
*[[G.984]] Gigabit-capable Passive Optical Networks ([[Passive Optical Network|GPON]])
*G.991.1 High bit rate Digital Subscriber Line (HDSL)
*[[ITU G.991.2|G.991.2]] Symmetric High-speed Digital Subscriber Line (G.SHDSL)
*[[ITU G.992.1|G.992.1]] [[ADSL]] (G.DMT)
*[[ITU G.992.2|G.992.2]] ADSL (G.Lite)
*[[ITU G.992.3/4|G.992.3/4]] ADSL2
*[[ITU G.992.5|G.992.5]] ADSL2+
*G.993.1 [[Very High Speed Digital Subscriber Line|VDSL]]
*[[ITU G.993.2|G.993.2]] [[Very High Speed Digital Subscriber Line 2|VDSL2]]
*G.1030 Estimating end-to-end performance in IP networks for data applications
*G.1040 Network contribution to transaction time
*G.1050 Network model for evaluating multimedia transmission performance over internet protocol
*[[Generic Framing Procedure|G.7041]] Generic Framing Procedure
*[[LCAS|G.7042]] Link Capacity Adjustment Scheme
*[[G.7043]] Virtual concatenation of plesiochronous digital hierarchy ([[Plesiochronous Digital Hierarchy|PDH]]) signals


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.<ref>http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p17)</ref>
===H - Audiovisual and multimedia systems===
*[[H.223]] Multiplexing protocol for low bit rate multimedia communication
* [[H.225.0]] protocol for call signaling, the media (audio and video), the stream packetization, media stream synchronization and control message formats. Formerly also included [[Real-time Transport Protocol|RTP]]
* [[H.235]] describes security in H.323
* [[H.239]] describes dual stream use in [[videoconferencing]], usually one for live video, the other for presentation
* [[H.245]] control protocol for multimedia communication
*[[H.261]] Video compression standard, circa 1991
*[[H.262]] Video compression standard (common text with part 2 of [[MPEG-2]]), circa 1994
*[[H.263]] Video compression standard, circa 1995
*[[H.264/MPEG-4 AVC|H.264]] Video compression standard (technically aligned with [[MPEG-4]] part 10), circa 2003
*[[H.320]] Narrow-band visual telephone systems and terminal equipment
*[[H.323]] Packet-based multimedia communications systems
** Annex D - Real-time facsimile over H.323 systems
** Annex G - Text conversation and Text SET
** Annex J - Security for H.323 Annex F
** Annex K - [[HTTP]] based service control transport channel in H.323
** Annex M.1 - Tunnelling of signalling protocol ([[QSIG]]) in H.323
** Annex M.2 - Tunnelling of signalling protocol ([[ISUP]]) in H.323
*[[H.324]] Terminal for low bit-rate multimedia communication
*[[H.332]] H.323 extended for loosely coupled conferences
* [[H.450]] describes the Supplementary Services in H.323


In the work of standardization ITU-T cooperates with other SDOs, i.e. the [[International Organization for Standardization]] (ISO) and the [[Internet Engineering Task Force]] (IETF)<ref>http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s10)</ref>
===I - Integrated services digital network (ISDN)===
See [[Integrated Services Digital Network]]


=== Development of Recommendations ===
===J - Transmission of television, sound programme and other multimedia signals===
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.<ref>http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s13-16), http://www.itu.int/ITU-T/info/tsb/info.html</ref>
===K - Protection against interference===
===L - Construction, installation and protection of cables and other elements of outside plant===
===M - TMN and network maintenance: international transmission systems, telephone circuits, telegraphy, facsimile and leased circuits===
See [[Telecommunications Management Network]]


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.<ref>http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s16), http://www.itu.int/ITU-T/studygroups/index.html</ref> 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.<ref>http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s23-24), http://www.itu.int/ITU-T/focusgroups/index.html</ref> Recent examples include work on [[Next Generation Networking]], Internet Protocol Television ([[IPTV]]) and digital identity management.<ref>http://www.itu.int/ITU-T/focusgroups/index.html</ref>
===N - Maintenance: international sound programme and television transmission circuits===
===O - Specifications of measuring equipment===
===P - Telephone transmission quality, telephone installations, local line networks===
*[[PSQM|P.861]] Perceptual Speech Quality Measure (PSQM)
*[[PESQ|P.862]] Perceptual Evaluation of Speech Quality (PESQ)


=== Approval of Recommendations ===
===Q - Switching and signalling===
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.
*[[Q.23]] [[Dual tone multi frequency]] access signalling
*[[Q.50]] Signalling between circuit multiplication equipments ([[DCME|CME]]) and international switching centres ([[International gateway exchange|ISC]])
*[[Q.700]] Introduction to [[CCITT]] [[Signalling System 7]]
*[[Q.701]] Functional description of the [[Message Transfer Part]] (MTP) of [[Signalling System 7]]
*[[Q.702]] [[Signalling (telecommunication)|Signalling]] data link
*[[Q.703]] Signalling link
*[[Q.704]] Signalling network functions and messages
*[[Q.705]] Signalling network structure
*[[Q.706]] [[Message Transfer Part]] signalling performance
*[[Q.707]] Testing and maintenance
*[[Q.708]] Assignment procedures for international signalling point codes
*[[Q.709]] Hypothetical signalling reference connection
*[[Q.710]] Simplified [[Message Transfer Part|MTP]] for small systems
*[[Q.711]] Functional description of the [[Signalling Connection and Control Part]]
*[[Q.712]] Definition and function of [[Signalling Connection and Control Part|signalling connection control part]] messages
*[[Q.713]] [[Signaling Connection and Control Part]] formats and codes
*[[Q.714]] Signaling Connection and Control Part procedures
*[[Q.715]] Signaling Connection and Control Part user guide
*[[Q.716]] Signaling Connection and Control Part performance
*[[Q.921]] Is the layer 2 standard for [[ISDN]] signalling
*[[Q.931]] Is the layer 3 standard for ISDN signalling
*[[Q.922-A]] Link Access Procedure Frame Bearer Services (LAPF)
*[[Q.933]] A frame relay interoperatability standard that adopted most of RFC 1490 recommendation


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.
===R - Telegraph transmission===


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.
In the UK, during the period of the Red Book, there was interest in the R series of Telegraph Transmission and indeed the modernisation of the UK Telex network took place based on the R101 standard to replace +-80 volt telex transmission in the "local line" copper network, and in R111 to replace the multiplexed transmission of telex over long distances using the developing digit transmission network. In the CCITT the development of R111 was finalised through the interest of the UK and USSR delegations.


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.
===S - Telegraph services terminal equipment===
===T - Terminals for telematic services===
*[[T.4]] Group 3 Apparatus for Transmission (aka Group 3 [[fax|faxes]])
*[[T.6]] Facsimile Coding Schemes and Coding Control Functions for Group 4 [[fax|Facsimile]] Apparatus. (aka Group 4 Compression)
*[[T.30]] Procedures for Document Facsimile Transmission. (T.30e defines colour faxing).
*[[T.31]] and [[T.32]] Provide an interface between fax machines and data terminals.
*[[T.120]] - Data protocols for multimedia conferencing
*[[Open Document Architecture|T.411 - T.424]] Comprise the [[Open Document Architecture]] (ODA and ODIF), a standardized [[document file format]]


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.
===U - Telegraph switching===
===V - Data communication over the telephone network===
{{main|ITU V-Series}}
*[[V.1]] Equivalence between binary notation symbols and the significant conditions of a two-condition code.
*[[V.5]] Standard that synchronous data signalling rates should be 600, 1200, 2400, 4800 and 9600 bit/s, to within better than 0.01%.
*[[V.10]] A recommendation, first agreed in 1976, for [[unbalanced]] electrical circuits for data communication at up to 100 [[Bit rate|kbit/s]].
*[[V.11]] A recommendation, first agreed in 1976, for [[Balanced line|balanced]] electrical circuits for data communication at up to 10 [[Bit rate|Mbit/s]].
*[[V.17]] A [[fax]] [[Protocol (computing)|protocol]] that uses [[Trellis modulation|TCM]] [[modulation]] at 12 and 14.4 kbit/s.
*[[V.21]] A recommendation for [[duplex (telecommunications)|full-duplex]] communication between two [[analog signal|analogue]] dial-up [[modem]]s using [[Audio frequency-shift keying|AFSK]] modulation at 300 [[baud]] to carry data at 300 bit/s.
*[[V.22]] A recommendation for full-duplex communication between two [[analog signal|analogue]] dial-up modems using [[Phase-shift keying|PSK]] modulation at 600 baud to carry data at 1200 or 600 bit/s.
*[[V.22bis]] An extension of V.22 using [[Quadrature amplitude modulation|QAM]] modulation at 600 baud to carry data at 2400 or 1200 bit/s, with fall-back to V.22 mode.
*[[V.23]] A recommendation for [[duplex (telecommunications)|half-duplex]] communication between two analogue dial-up modems using [[frequency-shift keying|FSK]] modulation at up to 600 or 1200 baud to carry digital data at up to 600 or 1200 bit/s respectively. An optional 75 baud reverse channel carries 75 bit/s.
*[[V.24]] A list of definitions for interchange circuits between [[data terminal equipment]] (DTE) and [[data circuit terminating equipment]] (DCE), first agreed in 1964. This is equivalent to a subset of [[Electronic Industries Alliance|EIA]] [[RS-232|RS 232]]: for the electrical and physical details, see [[V.28]] and others.
*[[V.25]] A recommendation, first agreed in 1968, for automatic calling and/or answering equipment on dial-up lines, using interchange circuits defined in V.24 specifically for parallel automatic calling. It includes procedures for disabling network echo cancellers and suppressors.
*[[V.25|V.25bis]] An extension of V.25 using the serial interchange circuits defined in V.24 for normal data transfer. Command formats are defined for asynchronous, and synchronous character- or bit-oriented ([[HDLC]]) operation.
*[[V.26]] A recommendation, first agreed in 1968, for full-duplex communication between two analogue fixed-line modems using [[Phase-shift keying|PSK]] modulation at 1,200 baud to carry synchronous data at 2400 bit/s. An optional 75 baud reverse channel carries 75 bit/s in either direction.
*[[V.26bis]] An extension of V.26, first agreed in 1972, for half-duplex operation of dial-up modems, adding a fall-back rate of 1200 bit/s (still at 1200 baud).
*[[V.26ter]] An extension of V.26, first agreed in 1984, for full-duplex fixed-line or dial-up operation to carry synchronous or asynchronous data with a fall-back rate of 1200 bit/s (at 1200 baud), separating channels by echo cancellation.
*[[V.27]] A recommendation, first agreed in 1972, for full-duplex or half-duplex communication between two analogue fixed-line modems using [[Phase-shift keying|PSK]] modulation at 1600 baud to carry synchronous data at 4800 bit/s. An optional 75 baud reverse channel carries 75 bit/s.
*[[V.27bis]] An extension of V.27, first agreed in 1976, adding a fall-back modulation rate, compatible with V.26, of 1200 bauds to carry data at 2400 bit/s. An adaptive equalizer is included to handle lower grade lines.
*[[V.27ter]] An extension of V.27bis for use on dial-up lines.
*[[V.28]] A recommendation, first agreed in 1972, for [[unbalanced]] electrical circuits for data communication. Together with the circuit specifications of V.24 and the 25-pin connector and pin assignments of IS 2110, this is compatible with [[Electronic Industries Alliance|EIA]] [[RS-232|RS 232]].
*[[V.29]] A recommendation, first agreed in 1976, for full-duplex communication between two analogue fixed-line modems using [[Quadrature amplitude modulation|QAM]] modulation at 2400 baud to carry synchronous data at 9600 bit/s. Fallback rates of 7200 and 4800 bit/s use 2400 baud at reduced modulations. Multiplexing of 7200, 4800 and 2400 bit/s subchannels up to an aggregate rate of 9600 bit/s is optional. An adaptation of this standard is used for facsimile (fax) transmission.
*[[V.32]] A recommendation, first agreed in 1984, for a family of [[duplex (telecommunications)|duplex]] analogue dial-up or fixed-line modems using [[Quadrature amplitude modulation|QAM]] modulation at 2400 baud to carry data at 9600/4800/2400 bit/s.
*[[V.32bis]] A duplex modem operating at data rates of up to 14.4 kbit/s for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits, with fallback to 12 kbit/s. This standard was improved on by modem manufacturers to create the V.terbo adhoc standard, signalling at 19.2 kbit/s, as suggestive of a V.32ter standard that never materialized.
*[[V.34]] is the ITU-T standard for full-duplex data communications up to 28.8 kbit/s with fallback to lower speeds depending on the [[remote]] modem and the conditions of the phone line. This standard was known informally as V.Fast, hence pre-standard modems called V.FC (V.FastClass).
*[[V.34]]bis A communications protocol for full-duplex datacommunications up to 33.6 kbit/s between two analog modems on dial-up lines.
*[[V.42]] Error correction protocol
*[[V.42bis]] [[Data compression]] procedures for [[data circuit terminating equipment]] (DCE) using error correction procedures to try to ensure the transfer of error-free data, even over the noisiest telephone lines. Ratified by CCITT in January 1990.
*[[V.44]] Data compression protocol
*[[V.90]] A digital modem and analogue modem pair for use on the Public Switched Telephone Network ([[PSTN]]) at data rates of up to 56 kbit/s downstream and up to 33.6 kbit/s upstream, using [[PCM]] encoding downstream, and [[QAM]] encoding upstream. V.90 Mode 2 used PCM upstream as well. This standard was known informally as V.Last and some pre-standard modems indicate V.Last compatibility or upgradeability. Prior to the arrival of the standard, there were two competing industry standards for 56 kbit/s downstream signalling, X2 and [[K56flex]]. K56flex itself is a merged standard of K56 and 56flex.
*[[V.92]] A digital modem and analog modem pair for use on [[Plain old telephone service|POTS]] at data signalling rates of up to 56 kbit/s downstream and up to 48 kbit/s upstream, using [[PCM]] encoding both ways, supporting Modem-on-Hold technology. This is a development of V.90 Mode 2.


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.
===X - Data networks and open system communication===
*[[X.1]] International user classes of service in, and categories of access to, public data networks and Integrated Services Digital Networks (ISDNs)
*[[X.3]] This is essentially a numbered list of terminal and comms setting attributes as used by a [[Packet Assembler/Disassembler]].
*[[X.21]] Interface between Data Terminal Equipment and Data Circuit-terminating Equipment for synchronous operation on public data networks
*[[X.25]] Interface between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) for terminals operating in the packet mode and connected to public data networks by dedicated circuit
*[[X.28]] Defines the character terminal interface to a Packet Assembler/Disassembler
*[[X.29]] Defines the [[X.25]] packet mode interface to a Packet Assembler/Disassembler
*[[X.75]] Interface between DCE units in a network. Essentially transport of X.25 messaging.
*[[X.110]] International routing principles and routing plan for public data networks
*[[X.121]] International numbering plan for public data networks. This can be seen as the specification for X.25 Addresses.
*[[X.200]] Information technology - [[Open Systems Interconnection]] - Basic Reference Model: The basic model
*[[X.208]] Specification of Abstract Syntax Notation One ([[ASN.1]]) (superseded by X.680)
*[[X.209]] Specification of Basic Encoding Rules for Abstract Syntax Notation One (ASN.1) (superseded by X.690)
*[[X.400]] Message handling services: Message handling system and service overview
*[[X.500]] Information technology - Open Systems Interconnection - The Directory: Overview of concepts, models and services Common text with ISO/IEC
*[[X.509]] Information technology - Open Systems Interconnection - The Directory: Public-key and attribute [[public key certificate|certificate]] frameworks
*X.520 Information technology &ndash; Open Systems Interconnection &ndash; The Directory - Selected Attribute Types
*X.521 Information technology &ndash; Open Systems Interconnection &ndash; The Directory - Selected Object Classes
*[[X.680]] series - [[ASN.1]] syntax specification
*X.690 series - ASN.1 encoding rules
* [[X.700]] Management framework for Open Systems Interconnection for CCITT applications
* X.701 Information technology — Open Systems Interconnection — Systems management overview
*[[X.800]] Security architecture for Open Systems Interconnection for CCITT applications


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.
===Y - Global information infrastructure and Internet protocol aspects===


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.<ref>http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s28-29), http://www.itu.int/ITU-T/e-flash/022-jan06.html</ref>
*[[ITU-T Recommendation Y.1720|Y.1720]] ''Protection switching for MPLS networks''
*[[ITU-T Recommendation Y.1730|Y.1730]] ''Requirements for OAM functions in Ethernet based networks''
*[[ITU-T Recommendation Y.1731|Y.1731]] ''OAM functions and mechanisms for Ethernet based networks''
*[[ITU-T Recommendation Y.17tor|Y.17tor]] ''Requirements for OAM function in [[T-MPLS]] based networks''
*[[ITU-T Recommendation Y.17tom|Y.17tom]] ''Operation & Maintenance mechanisms for [[T-MPLS]] layer networks''


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).<ref>http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s27), http://www.itu.int/ITU-T/e-flash/022-jan06.html</ref>
===Z - Languages and general software aspects for telecommunication systems===


== Series and Recommendations ==
* Z.100 [[Specification and Description Language]] (SDL)
ITU-T issues Recommendations that have names like [[X.500]], 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.
* Z.120 [[Message Sequence Chart]] (MSC)
* Z.130 [[Extended Object Definition Language]] (eODL)
* Z.140 [[TTCN|Testing and Test Control Notation]] (TTCN)
* Z.150 [[User Requirements Notation]] (URN)
* Z.200 [[CHILL|CCITT High Level Language]] (CHILL)


=== International Telecommunication Regulations (ITRs) ===
==See also==
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).<ref>http://www.itu.int/ITU-T/itr/files/ITR-e.doc</ref>


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.<ref>http://www.itu.int/ITU-T/itr-eg/</ref>
* Other specifications which are numbered similarly to ITU-T Recommendations, but are not products of the ITU-T, include:

**[[X10 (industry standard)|X10]] Interface between Home Automation devices
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.<ref>http://www.itu.int/osg/spu/stratpol/ITRs/auth/itr-03.doc</ref>
**[[Electronic Data Interchange]] ANSI Standard

**[[ITU-R]] Recommendations, such as M.1457
=== Key Achievements of ITU ===
* (x)[[DSL]] (Digital Subscriber Line) series of standards for broadband
* [[ASN.1]]
* Audio coding [[G.711]] and G.72x series
* International Emergency Preference Scheme E.106
* Numbering plan [[E.164]]
* Fax standards T.2 – T.4, [[T.30]], [[T.37]], [[T.38]]
* [[H.323]] family of standards for multimedia
* Image coding [[JPEG]] T.80 and T.800 series
* IMSI codes used in SIM cards [[E.212]]
* Interconnection rate harmonization
* ISDN [[Q.931]]
* [[Passive optical network]]s (PON) G.983.1, G.984.1/2
* [[Public Key Infrastructure]] (PKI) [[X.509]]
* [[Synchronous Digital Hierarchy]] (SDH) [[G.707]] – G.803
* Security framework X.805
* [[Signalling System 7]] Q.7xx series
* Standards relating to [[Quality of Service]] (QoS)
* Video coding [[H.262]]/MPEG2-Video and [[H.264]]/MPEG-4 AVC
* Wave-division multiplexing (WDM)
* [[X.25]]

== 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. Find out more about the work [http://www.itu.int/ITU-T/gap/ here].

* The [http://www.itu.int/ITU-T/studygroups/com17/ict/index.html 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 ==
* [[International Telecommunication Union]]
* [[:Category:ITU-T recommendations]]
* [[:Category:ITU-R recommendations]]
* [[World Summit on the Information Society]]

== References ==
{{reflist}}


== External links ==
== External links ==
* [http://www.itu.int/ International Telecommunication Union (ITU) (official site)]
* [http://www.itu.int/ITU-T/ ITU Standardization Sector (ITU-T)]
* [http://www.itu.int/ITU-R/ ITU Radiocommunication Sector (ITU-R)]
* [http://www.itu.int/ITU-D/ ITU Development Sector (ITU-D)]


* [http://www.itu.int/ITU-T/ Official ITU-T website]
* [http://www.itu.int/ITU-T/studygroups/ ITU-T Study Groups]
* [http://www.itu.int/ITU-T/publications/recs.html List of all ITU-T Recommendations]
* [http://www.itu.int/ITU-T/focusgroups/index.html ITU-T Focus Groups]
* [http://www.itu.int/ITU-T/publications/recs.html ITU-T Recommendations]
* [http://www.3amsystems.com/wireline/hmo.htm 3am Systems - Wireline Modems V.xx Modulations]
* [http://www.itu.int/ITU-T/newslog/ ITU-T Newslog (RSS available)]
* [http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf ITU-T Guide for beginners (PDF)]
* [http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf 50 years of CCITT/ITU-T (PDF)]


{{Compression Formats}}
{{Compression Formats}}

Revision as of 15:21, 19 October 2007

The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland.

The standardization work of ITU dates back to 1865, with the birth of the International Telegraph Union. It became a United Nations specialized agency in 1947, and the International Telegraph and Telephone Consultative Committee (CCITT), (from the French name "Comité Consultatif International Téléphonique et Télégraphique") was created in 1956. It was renamed ITU-T in 1993.[1]

ITU has been an intergovernmental public-private partnership 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.[2]

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.[3]

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 only become mandatory 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.[4]

History

Although the ITU itself dates back to 1865[5], 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).[6]

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).[7]

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) and the Telecommunication Development Sector (ITU-D).[8]

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.[9]

"Real time" standardization

The rise of the personal computer industry in the early 1980s created a new common practice among both consumers and businesses of adopting "bleeding edge" communications technology even if it was not yet standardized. Thus, standards organizations had to put forth standards much faster, or find themselves ratifying de facto standards 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.[10] New and updated Recommendations are published on an almost daily basis, and the entire library of over 3’270 Recommendations is now free of charge online.

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.[11]

In the work of standardization ITU-T cooperates with other SDOs, i.e. the International Organization for Standardization (ISO) and the Internet Engineering Task Force (IETF)[12]

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.[13]

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.[14] 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.[15] Recent examples include work on Next Generation Networking, Internet Protocol Television (IPTV) and digital identity management.[16]

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.[17]

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).[18]

Series and Recommendations

ITU-T issues Recommendations that have names like X.500, 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.

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).[19]

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.[20]

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.[21]

Key Achievements of ITU

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. Find out more about the work here.
  • 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

References

  1. ^ http://www.itu.int/net/about/landmarks.aspx
  2. ^ http://www.itu.int/net/about/index.aspx
  3. ^ http://www.itu.int/ITU-T/info/index.html
  4. ^ http://www.apdip.net/publications/iespprimers/eprimer-igov.pdf (p13)
  5. ^ http://www.itu.int/net/about/history.aspx
  6. ^ http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p8)
  7. ^ http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p8)
  8. ^ http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p14)
  9. ^ http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf
  10. ^ http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p16)
  11. ^ http://www.itu.int/ITU-T/50/docs/ITU-T_50.pdf (p17)
  12. ^ http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s10)
  13. ^ http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s13-16), http://www.itu.int/ITU-T/info/tsb/info.html
  14. ^ http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s16), http://www.itu.int/ITU-T/studygroups/index.html
  15. ^ http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s23-24), http://www.itu.int/ITU-T/focusgroups/index.html
  16. ^ http://www.itu.int/ITU-T/focusgroups/index.html
  17. ^ http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s28-29), http://www.itu.int/ITU-T/e-flash/022-jan06.html
  18. ^ http://www.itu.int/dms_pub/itu-t/oth/0A/0F/T0A0F0000090001PDFE.pdf (s27), http://www.itu.int/ITU-T/e-flash/022-jan06.html
  19. ^ http://www.itu.int/ITU-T/itr/files/ITR-e.doc
  20. ^ http://www.itu.int/ITU-T/itr-eg/
  21. ^ http://www.itu.int/osg/spu/stratpol/ITRs/auth/itr-03.doc
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