A standard for facsimile transmission at 64 Kbps

Refers to the ITU specification for fax machines that transmit over digital networks, e.g., ISDN (Group 3 fax machines transmit over standard analog phone lines.) A Group 4 fax can communicate at 64 Kbps or 1.5 seconds per page.

T.6 standards for facsimile devices developed by CCITT. Using Public Data Networks or modified PSTN, the data is transmitted using ECM (Error Correction Mode).

A high-speed (56 kbps) facsimile protocol specific to ISDN.