The root cause of the issue is that the terminating fax tone is interpreted as a modem tone by the local DSP.
Tier4 recommendation is that ip-codec-sets have either fax or modem capabilities, but not both. Ideally modems and fax machines should have unique network regions and codec sets.
For internal calls where an IGC connection is made between PN and/or MG, the CM always uses Avaya proprietary fax pass thru mode. Hence, internal fax (same MG/PN), IGC fax internal or out PRI, etc are not impacted and complete as expected.
For outgoing SIP fax calls, the network region is determined by the signaling group's far-end network region. The ip-codec-set used is determined by ip-network-region based on the signaling group's far-end NR and the originator's NR.
For incoming SIP fax calls, the network region of the far-end is determined in order of precedence: presence of SDP media IP in ip-network-map, then the far-end NR from the SIP trunk signaling group, then the near-end NR.
If this does not work especially for analog endpoints if other end will never need fax or modem make the following changes.
On the SIP trunk group page 2 in the field XOIP Treament set to TTY
On the station page for analog extensions such as conference room speaker phones on page 1 set the field XOIP Endpoint Type to TTY.
This will allow TTY devices to still function on the trunk groub, but not modems and fax machines.
