i have asterisk 1.4.20 with freepbx connected to avaya s8400 through h323, i am unable to send and receive faxes, any advise?
You have a very old version of Asterisk and you did not tell us if/what version of FreePBX.
You also did not tell us how you wanted to do the FAX (IE: analog FAX to FXO port, FAX to email.) or what protocol (t.38 or inband).
Asterisk by itself can’t do much of any faxing. Various fax modules exist, most for later versions.
sorry for late reply, but the i have upgraded asterisk to 1.4.44, and change T.38 settings to OFF in Avaya CM, and i can send and receive faxes now normally