System information

Table 19-1. Possible values for the faxdetect option in chan_dahdi.conf
Value Description
incoming Enables fax detection on inbound calls. When a fax is detected, applies the faxbuffers option if it has been
set and redirects the call to the fax extension in the dialplan. For more information on the faxbuffers option,
see “Using Fax Buffers in chan_dahdi.conf” on page 454.
outgoing Enables fax detection on outbound calls. The dialplan is not executing on an outbound channel. If a fax is detected,
the faxbuffers option will be applied and the channel will be redirected and start executing the dialplan at
the fax extension.
both Enables fax detection for both incoming and outgoing calls.
no Disables fax detection. This is the default.
To enable fax detection for SIP calls, you must set the faxdetect option in /etc/asterisk/
sip.conf. This option may be set in the [general] section, or for a specific peer.
Table 19-2 covers the possible values for the faxdetect option in sip.conf.
Table 19-2. Possible values for the faxdetect option in sip.conf
Value Description
cng Enables fax detection by watching the audio for a CNG tone. If a CNG tone is detected, redirects the call to the fax
extension in the dialplan.
t38 Redirects the call to the fax extension in the dialplan if a T.38 reinvite is received.
yes Enables both cng and t38 fax detection.
no Disables fax detection. This is the default.
Outgoing Fax Handling
Transmitting faxes from Asterisk is somewhat more difficult than receiving them. The
reason for this is simply due to the fact that the preparation of the fax prior to trans-
mission involves more work. There isn’t anything particularly complex about fax trans-
mittal, but you will need to make some design decisions about things like:
• How to get the source fax file formatted for Asterisk
• How to get the source fax file onto the Asterisk system (specifically, into some
folder where Asterisk can access it)
• What to do with transmitted faxes (save them? delete them? move them some-
where?)
• How to handle transmission errors
Outgoing Fax Handling | 449