Digital transmission standard for fax devices

Standard created by the International Telecommunication Union Telecommunications relating to Fax devices. A Group 3 fax device is a digital machine containing a 14400 baud modem that can send an 8 1/2 by 11-inch page in approximately 20 seconds with a resolution of either 203 by 98 dots per inch or 203 by 196 dpi - fine - using Huffman code to compress fax data.

Refers to the ITU specification for fax machines that use digital encoding. Encoding methods for Group 3 fax machines include MH (Modified Huffman), MR (Modified Read) and MMR (Modified Modified Read). If a fax is said to be "Group 3 compatible" this means that the unit will communicate with virtually all other installed fax machines. A Group 3 fax machine equipped with a 33.6 Kbps modem can transmit a page at 3 seconds per page (based on the ITU-T Test Chart #1 in Standard resolution, and not including the handshake). Older analog Group 1 and Group 2 fax machines are obsolete.

This is a standard for facsimile communications over analog telephone lines originally approved by the CCITT in its T.4 and T.30 recommendations in 1980. This standard is supported by almost all of the current install base of fax machines and fax devices and is continuing to be updated.