CCITT

Abbreviation of Comit Consultatif International T l phonique et T l graphique, an organization that sets international communications standards. CCITT, now known as ITU(the parent organization) has defined many important standards for data communications, including 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 400 protocol supports images of up to 400 dpiresolution.
  • V.21: The standard for full-duplex communication at 300 baud in Japan and Europe. In the United States, Bell 103is 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 212Ais more common.
  • V.22bis : The worldwide standard for full-duplex modems sending and receiving dataacross 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.34 :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 MNPfor 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-switchingprotocol 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.
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