.Data transmission rate

Several different telephone line modulation techniques are used by fax machines. They are negotiated during the fax-modem handshake, and the fax devices will use the highest data rate that both fax devices support, usually a minimum of 14.4 kbit/s for Group 3 fax.
ITU Standard
Released Date
Data Rates (bit/s)
Modulation Method
V.27
1988
4800, 2400
PSK
V.29
1988
9600, 7200, 4800
QAM
V.17
1991
14400, 12000, 9600, 7200
TCM
V.34
1994
28800
QAM
V.34bis
1998
33600
QAM
Note that 'Super Group 3' faxes use V.34bis modulation that allows a data rate of up to 33.6 kbit/s.