[RESOLVED] Unable to execute SendFAX with multiple files


I’m trying to send fax from Asterisk 13.1-cert2 using res_fax and res_fax_spandsp.

It works fine when sending a single tif file but I would need to be able to send multiple files. E.g. a generic header page followed by a page with more specific content.

I set up a simple test in extensions.conf

exten => s,1,SendFAX(/var/asterisk/linehandler/faxpage1.tif&/var/asterisk/linehandler/faxpage2.tif,d)
exten => s,n,Hangup

And I execute it from Asterisk CLI with the following command (output included)
*CLI> channel originate SIP/f_digium_fax/0709931762 extension s@test_fax
== Using SIP RTP CoS mark 5
– Called f_digium_fax/0709931762
– SIP/f_digium_fax-00000000 is making progress
– SIP/f_digium_fax-00000000 is ringing
– SIP/f_digium_fax-00000000 answered
– Executing [s@test_fax:1] SendFAX(“SIP/f_digium_fax-00000000”, “/var/asterisk/linehandler/faxpage1.tif&/var/asterisk/linehandler/faxpage2.tif,d”) in new stack
– Channel ‘SIP/f_digium_fax-00000000’ sending FAX:
– /var/asterisk/linehandler/faxpage1.tif
– /var/asterisk/linehandler/faxpage2.tif
[Feb 15 20:03:51] ERROR[16944][C-00000000]: res_fax.c:1174 fax_session_reserve: Could not locate a FAX technology module with capabilities (SEND,MULTI_DOC)
[Feb 15 20:03:51] ERROR[16944][C-00000000]: res_fax.c:2729 sendfax_exec: Unable to reserve FAX session.
== Spawn extension (test_fax, s, 1) exited non-zero on ‘SIP/f_digium_fax-00000000’

It seems as I’m missing fax capability for MULTI_DOC

*CLI> fax show capabilities

Registered FAX Technology Modules:

Type : Spandsp
Description : Spandsp FAX Driver
Capabilities : SEND RECEIVE T.38 G.711 GATEWAY

1 registered modules

To me it seems as res_fax_spandsp does not support sending multiple documents? Is that correct or am I doing something wrong?

I also tried a different approach in extensions.conf
exten => s,1,SendFAX(/var/asterisk/linehandler/faxpage1.tif,d)
exten => s,1,SendFAX(/var/asterisk/linehandler/faxpage2.tif,d)
exten => s,n,Hangup

I this case the first SendFAX is successfull but the receiving side is hanging up so the negotiation for the second SendFAX failes.
This sounds as a correct behaviour to me. The receiver does not expect a new fax session during the same call.
Should I expect different behaviour in this case?
I found a topic related to this but unfortunatly there were no answers to it.
See res_fax: Errors when sending multiple documents

Based on the above information I don’t know how to proceed. Is there any other FAX module available? res_fax_digium is not supported in Asterisk 13 so I guess thats not an option.

I appreciate all kind of feedback in this matter.

My setup is Asterisk 13.1-cert2 running on Debian (Jessie) OS.
Using SIP from Asterisk to a local Digium G100 gateway with a E1 PRI connection directly to our telecom provider.

Kind regards,


The spandsp module does not have support for joining TIFF files like this as part of the SendFAX operation. You will need to do it externally and feed it only a single TIFF.

Thanks for the reply!