[asterisk-users] FAX CNG detected but no fax extension

[Harel]

Hello,
I have a question regarding incoming fax to local file (on the Asterisk server).
While the fax is received properly (I have the tiff file generated as expected) I get the warning 'FAX CNG detected but no fax extension' on the consol.

If the fax is received ok then what 'fax extension' does it expect and what should I do there? 

My Setup:
Sender -> Public PSTN -> provider -> SIP trunk (configured with G711a) -> Asterisk (13.6.0)

My extension.conf on relevant section is this (obviously this is not production code):
exten => s,1,Answer()
same =>      n,Verbose(0, Attempt to Receive FAX)
same =>      n,Set(FAXOPT(gateway)=no)
same =>      n,ReceiveFax(/var/workspace/testfax.tiff,d)
same =>      n,Hangup()

and 
Server*CLI> module show like fax
Module                         Description                              Use Count  Status      Support Level
res_fax.so                     Generic FAX Applications                 1          Running              core
res_fax_spandsp.so             Spandsp G.711 and T.38 FAX Technologies  0          Running          extended
2 modules loaded

Thank you for your assistance,

Kind Regards,
Harel Cohen