[asterisk-users] Questions about fax detection

Olivier oza_4h07 at yahoo.fr
Thu Sep 13 02:47:28 CDT 2012


I want to offer SIP phone user a "custom fax-to-email" feature.
Here is how I would describe this feature:

- for every SIP phone,a custom email address is defined
- when a SIP phone answers an incoming call (from a trunk or another SIP
endpoint), it detects the call is coming from a fax machine and then :
+ it plays a pre-recorded audio file to the receiving user ("You are now
receiving a fax call, please check you email box")
+ while at the same time, the incoming channel is forwarded to an
appropriate statement within Asterisk dialplan.
- when an unanswered call is forwarded to a voicemail, the fax call is also
detected and teated appropriately.

1. It is possible to play a pre-recorded audio file to the receiving user ?
If positive, how can it be done ?

2. What is the exact purpose of sip.conf faxdetect setting in this case
given the assumption "faxdetect is set to yes in general section of
I would say the following applies:
"faxdetect for the incoming channel has no influence at all.
If faxdetect is set to yes or unset in the outgoing channel, then Asterisk
will jump to fax extension.
If faxdetect is set to no in the outgoing channel, then Asterisk will jump
to fax extension."

Do you agree ?

3. Using CLI, is there a way to read the faxdetect parameter value of a
given SIP peer ?
To me "sip show peer <foo>" doesn't (seem to) display this.

4. When I type "fax show settings" in, I've got (on an Asterisk 10 box):
CLI> fax show settings
FAX For Asterisk Settings:
    ECM: Enabled
    Status Events: Off
    Minimum Bit Rate: 2400
    Maximum Bit Rate: 14400
    Modem Modulations Allowed: V17,V27,V29

FAX Technology Modules:

Spandsp (Spandsp FAX Driver) Settings:

This last line troubles me a little (did I forget to configure spandsp ?).
Should I care ?

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