[Asterisk-Users] FAX over SIP

[Steven Critchfield]

On Thu, 2003-09-04 at 01:18, Ing. Angel Gomez Garcia wrote:
>     Hello.
> 
>     Has someone been able to make work faxes over sip, i have one mp108 
> fxo and one mp108 fxs, my  setup is :
> 
> telco analog line -----> mp108fxo -----> Asterisk ------> mp108fxs 
> -------> fax machine
> 
> 1) Asterisk detects the tone from the sending fax ( i am receiving ) but 
> looks for extension 'ff' not 'fax', ( at least that's what * complaint, 
> invalid extension ff in context ).
> 
> 2) I add 'ff' extension and dial to SIP/faxdev, Asterisk routes the call 
> to this extension but when the fax answers the call is dropped ( don't 
> have here the SIP debug output ) but seems that when * tries to make the 
> bridge the mp108 fxo sends a BYE.
> 
> 3) I dialed in to * with a phone ( external line and internal extension 
> ) and dial extension for the fax and i cann hear the fax, so the call is 
> not dropped, the bridge is established successfully.
> 
> 4) If I pickup the call on the fax machine ( it has a phone set ) and 
> then pressed the 'start' button to start de fax receiver, then, the two 
> faxes talked to each other and the fax is received well.

By listening to #4 it sounds like you answered your own question, yes it
is possible. Now you need to find out why in #2 that it sends a bye. My
guess is that you have a difference in the dial command options that
keep asterisk listening to the line when dialing the extension that
isn't there on the ff extension. This may have asterisk trying to issue
a reinvite to connect the call legs together without asterisk in the
middle. This is causing the BYE, and then everything fall apart. Maybe
you need to make sure the canreinvite is turned off for this device in
the sip.conf and try some more. 

>     Seems that the problem is only when the fax answer automatically ( 
> could be the tones the receiving fax plays ? ), the same problem happens 
> when i try to use hylafax to receive the fax.
> 
>     Any hints ?
> 
>     Thank's.
> 
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-- 
Steven Critchfield <critch at basesys.com>