asterisk users - Jan 2015 - Dialplan for receiving faxes on Asterisk

Hi all,

It looks like people commonly use this kind of dialplan when receiving
faxes on Asterisk, with a jump to extension fax during the Wait() if a fax
tone is detected:

[start-here]
exten => _X.,1,Answer()
exten => _X.,n,Wait(n)
exten => _X.,n,...do stuff...
exten => _X.,n,Hangup()

exten => fax,1,Goto(fax-rx,receive,1)

[fax-rx]
exten => receive,1,...
exten => receive,n,...do stuff...
exten => receive,n,ReceiveFAX()

This is well suited in case Asterisk needs to receive both voice and fax
calls. But what if Asterisk is only used to receive fax calls, can we start
directly at the fax-rx context? I've heard that it's better to wait a
few
seconds before calling ReceiveFAX(), is it still necessary in case we don't
actually need fax detection?

Simon
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On 30/01/2015 1:25 PM, Simon Humbert wrote:
>   Hi all,
>
> It looks like people commonly use this kind of dialplan when receiving
> faxes on Asterisk, with a jump to extension fax during the Wait() if a
> fax tone is detected:
>
> [start-here]
> exten => _X.,1,Answer()
> exten => _X.,n,Wait(n)
> exten => _X.,n,...do stuff...
> exten => _X.,n,Hangup()
>
> exten => fax,1,Goto(fax-rx,receive,1)
>
> [fax-rx]
> exten => receive,1,...
> exten => receive,n,...do stuff...
> exten => receive,n,ReceiveFAX()
>
> This is well suited in case Asterisk needs to receive both voice and fax
> calls. But what if Asterisk is only used to receive fax calls, can we
> start directly at the fax-rx context? I've heard that it's better
to
> wait a few seconds before calling ReceiveFAX(), is it still necessary in
> case we don't actually need fax detection?
>
If you don't have the need to detect the fax tone then I don't see any 
need to wait.

You should disable the 'faxdetect' option in your peer otherwise it may 
attempt to redirect to the 'fax' extension upon detecting the fax 
signalling.

Assuming you are using a SIP trunk to accept the call you could use in 
your sip.conf peer something like;

context=fax-rx
disallow=all
allow=alaw,ulaw
jbenable=no
faxdetect=no
directmedia=no
callbackextension=receive
t38pt_usertpsource=yes
encryption=no

Note, in this example I am using 'callbackextension' instead of 
'register =>', refer to the default sip.conf for further information.

Larry.