I have tested this with current versions...
ok so unlike many others... I find G711 gives better faxing than T.38
( for many reasons... but mainly because all my network is fibre and I control a lot of it myself ).
I have one carrier that that insists on doing fax tone detection in their SBC.
the call comes in G711... they detect fax tones then re-invite T.38.
I want to knock the T.38 back, but cant..
if I disable T.38 we get the 100 Trying... then nothing further.
only way I can inter-op is to use t38.