FAX Calls do not work


two FAX maschines are connected to FreePBX.
FAX1 one calls FAX2.
Incoming INVITE to FreePBX contains SDP Parameter among other things:

“Media Attribute (a): gpmd:97 vbd=yes”

In outgoing INVITE SDP Parameters are completely changed
and above Attribute is missing.

What has to be changed in FreePBX, that all incoming SDP Parameters are transfered to the outgoing side?