CCITT
Last modified: Wednesday, May 23, 2001
Abbreviation of C omité C onsultatif I nternational T éléphonique et T élégraphiquecommunications 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 V.42bis: A data compression protocol that can enable modems to achieve a data transfer rate of 34,000 bps. V.90 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.
CCITT standard fax images These downloadable images are available for testing fax compression.
