Im having Asterisk Free PBX with chan_sip channel. Could you please confirm, whether Asterisk supports hs-redundancy and ls-redundancy pass-through in T.38 Fax signaling.
Enabled setting in PBX is “T.38 fax pass-through = yes with redundancy”
I can also see PBX forwards hs-redundancy value, if it received from Fax client. But when PBX receives ls-redundancy, PBX reset it to 0 and forward to upstream.