Yours, Etc.: Origins and Uses of 8 Sign-Offs
(G4) The CCITT fax protocol which uses data compression and allows a variety of file types (e-mail, pictures, PostScript, etc.) to be transmitted over digital (ISDN) telephone lines.
The Group 4 protocol was published by CCITT in 1993. Full details of the protocol are available from ITU-T.
See also Group 3.