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CCITT


Abbreviation of Comité Consultatif International Téléphonique et Télégraphique, 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 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 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.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 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.






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