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

Tech Support asterisk at voipbusiness.us
Tue Nov 29 09:34:49 CST 2016

    Just an FYI, in the dialplan below, The ReceiveFax() application
receives the fax document and then automatically hangs up the call when it
is finished. That means Asterisk will then jump to the hangup extension in
the same context (if it exists) without executing any lines of code after
the ReceiveFax line (the Hangup() never gets executed).
John V.   

-----Original Message-----
From: asterisk-users-bounces at lists.digium.com
[mailto:asterisk-users-bounces at lists.digium.com] On Behalf Of Harel
Sent: Tuesday, November 29, 2016 7:00 AM
To: asterisk-users at lists.digium.com
Subject: [asterisk-users] FAX CNG detected but no fax extension

I have a question regarding incoming fax to local file (on the Asterisk
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

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()

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

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