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.