ITU Standards for Data Communications

Short for International Telecommunication Union, an intergovernmental organization through which public and private organizations develop telecommunications. The ITU was founded in 1865 and became a United Nations agency in 1947. It is responsible for adopting international treaties, regulations and standards governing telecommunications. The standardization functions were formerly performed by a group within the ITU called CCITT, but after a 1992 reorganization the CCITT no longer exists as a separate body.

• 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 196l.
• Group 4: A protocol for sending fax documents over ISDN networks. The Group 400 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, the Bell 103 is used in place of V.21.
• V.22: Pronounced V- dot -twenty-two. V.22 is short for the CCITT V.22 communications. 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: Pronounced V- dot -twenty-two-biss, V.22bis is short for the CCITT V.22bis communications. The worldwide 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 is the protocol 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.32: The standard for full-duplex modems sending and receiving data across phone lines at up to 28,800 BPS V.34 modems 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. See MNP for a competing standard.
• 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 phone lines at up to 56,600 BPS
• X.25: The most popular packet-switching protocol for WANs.
• 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.

Communications Protocols