Source : Free On-Line Dictionary of Computing

Group 4
     
         (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}.
     
        (1998-09-10)