Indicates the ITU-T communication mode supported by the machine. There are four standard modes: Group 1 (G1) mode, which is also referred to as 6-minute FM mode, was used on the first generation of analog machines; Group 2 (G2) mode, which is faster and more automated than Group 1 machines, was used on the second-generation analog machines; Group 3 (G3) mode, which supports bit-per-second rates up to 14.4 Kbps, is the first mode to utilize digital technology. Many Group 3 machines are also compatible with the older Group 2 and Group 1 machines. G3 is the most common mode presently in use. Group 4 (G4) mode is the latest standard. It is designed for high-speed communication (up to 64,000 bps) and must be used on private or special digital (as opposed to analog) telephone lines.