I have some problem with fax.
Outgoing Fax not issue, but Incoming fax issue with error SIP/2.0 488 Not Acceptable Media.
Please see my debug and configuration.
The incoming dial peer does not support fax:
dial-peer voice 1 voip description INCOMING FROM PSTN SBC translation-profile incoming PSTN-inbound session protocol sipv2 incoming called-number . voice-class codec 1 dtmf-relay h245-alphanumeric rtp-nte no vad
Hence when the outgoing leg sends a REINVITE to renegotiate fax, we reject that leg with 488.
My problem has been solve, after discussions with ISP.
ISP try to change configure and enable feature T38 or fallback g711.