ITU-T is the telecom standardization organization of the International Telecommunication Union (ITU). It was previously known as CCITT, or Comité Consultatif International Téléphonique et Télégraphique (Consultative Committee for International Telegraphy and Telephony).
Series and Recommendations
ITU-T issues recommendations that have names like X.500, where X is the series and 500 is a serial number.
V.24 List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit terminating equipment (DCE) - equivalent to EIARS 232, defined in ISO 2110, circa 1964
V.25 Protocol for automatic calling and/or answering equipment on dialup lines, circa 1968
V.29 A comminications protocol allowing two fax to signal each other at 9600 bit/s
V.32 A family of 2-wire, duplexmodems operating at data signalling rates of up to 9600bit/s, full duplex for use on the general switched telephone network and on leased telephone-type circuits.
V.32bis A duplex modem operating at data signalling rates of up to 14 400 bit/s for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits, with fallback to 12000 bits/s. This standard was improved on by modem manufacturers to create the V.terbo adhoc standard, signalling at 19,2 kb/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 28,000bit/s with fallback to lower speeds depending on the remote modem ant 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+]] (aka V.34bis) A communications protocol for full-duplex datacommunications up to 33,6 kb/s between two analog modems on dial-up lines.
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.90 A digital modem and analogue modem pair for use on the Public Switched Telephone Network (PSTN) at data signalling rates of up to 56 000 bit/s downstream and up to 33 600 bit/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 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.
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.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.110 International routing principles and routing plan for public data networks
X.121 International numbering plan for public data networks
X.200 Information technology - Open Systems Interconnection - Basic Reference Model: The basic model
X.208 Specification of Abstract Syntax Notation One (ASN.1)
X.209 Specification of Basic Encoding Rules for Abstract Syntax Notation One (ASN.1)
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 certificate frameworks
X.520 Information technology – Open Systems Interconnection – The Directory - Selected Attribute Types
X.521 Information technology – Open Systems Interconnection – The Directory - Selected Object Classes
Y - Global information infrastructure and Internet protocol aspects
Z - Languages and general software aspects for telecommunication systems
AAA
See also
Other specifications which are numbered similar to ITU-T recommendations, but are not products of ITU-T, include:
In 1984, the CCITT developed a specification defining the facsimile coding schemes to be used in the Group 4 fl and white facismile.
The advantage of the CCITT T.6 coding scheme over the one-dimensional coding scheme of Group 3 facsimile is that it exploits both horizontal and vertical dependencies, resulting in the greater compression efficiency.
Since the CCITT T.4 two-dimensional coding scheme requires that every Kth line of image data must be encoded by the one-dimensional coding scheme, it is less efficient compared to the CCITT T.6 coding scheme.
Feeds |
Contact