CCITT

Overview

CCITT is the acronym for Comitè Consultatif Internationale de Tèlègraphie et Tèlèphonie (now called the Telecommunications Standardization Sector (ITU-T)). It is “[t]he internationally recognized French acronym for the International Telegraph and Telephone Consultative Committee, one of the former sub-entities of the International Telecommunications Union (ITU).”

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The CCITT (ITU-T) is responsible for developing international telecommunications recommendations relating to standardization of international telecommunications services and facilities, including matters related to international charging and accounting principles and the settlement of international telecommunications accounts.

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“Such recommendations are, effectively, the detailed implementation provisions for topics addressed in the International Telecommunication Regulations (ITR).

Standards

This group sets international standards for the following:

• Group 3: The universal protocol for sending fax documents across telephone lines. The Group 3 protocol specifies CCITT T.4 data compression and a maximum transmission rate of 9,600 baud. There are two levels of resolution: 203 by 98 and 203 by 196.

• Group 4: A protocol for sending fax documents over ISDN networks. The Group 4 protocol supports images of up to 400 dpi resolution.

• V.21: The standard for full-duplex communication at 300 baud in Japan and Europe. (In the United States, Bell 103 is used in place of V.21.)

• V.22: The standard for half-duplex communication at 1,200 bps in Japan and Europe. (In the United States, the protocol defined by Bell 212A is more common.)

• V.22bis: The standard for full-duplex modems sending and receiving data across telephone lines at 1,200 or 2,400 bps.

• V.29: The standard for half-duplex modems sending and receiving data across telephone lines at 1,200, 2,400, 4,800, or 9,600 bps. This protocol is used by fax modems.

• V.32: The standard for full-duplex modems sending and receiving data across phone lines at 4,800 or 9,600 bps. V.32 modems automatically adjust their transmission speeds based on the quality of the lines.

• V.32bis: The V.32 protocol extended to speeds of 7,200, 12,000, and 14,400 bps.

• V.34: The standard for full-duplex modems sending and receiving data across telephone lines at up to 28,800 bps. V.34 [[modem]s automatically adjust their transmission speeds based on the quality of the lines.

• V.42: An error-detection standard for high-speed modems. V.42 can be used with digital telephone networks.

• V.42bis: A data compression protocol that can enable modems to achieve a data transfer rate of 34,000 bps.

• V.90: The standard for full-duplex modems sending and receiving data across telephone lines at up to 56,600 bps.

• V.92: The enhanced standard for V.90.

• X.25: The most popular packet-switching protocol for LANs. Ethernet, for example, is based on the X.25 standard.

• X.400: The universal protocol for e-mail. X.400 defines the envelope for e-mail messages so all messages conform to a standard format.

• X.500: An extension to X.400 that defines addressing formats so all e-mail systems can be linked together.