I have several customers who for some reason with the far side’s carrier cannot fax properly over t.38. We found the only other solution was to use a trunk that we do not pay extra for t.38 outbound guaranteed routes. The issue we have is even the routes we pay with our carrier can sometimes negotiate t.38 depending on which provider is used to make the call. What I would like to do to guarantee we can always fax to these people is configure a SIP trunk’s PEER details with t38pt_udptl=no… but I can still see t.38 negotiation occurring… How can I disable t38 passthrough per trunk without killing the entire system? We also still want to keep t38 enabled per extension for all the other fax numbers that work without any issues.
Is this possible?