Could not locate a FAX technology module with capabilities

[rcarsey1]

I recently forklift upgraded Asterisk from v11 to v20.0.0 and have switched everything over to PJSIP. However, I’m a little lost when it comes to fax …

When I dial an extension which my Avaya PBX forwards over to Asterisk via PJSIP, I’m getting the following errors:

-- Executing [5577@from-avaya:1] Set("PJSIP/Avaya-00001788", "FILENAME=fax-20250217-134335.tif") in new stack
-- Executing [5577@from-avaya:2] ReceiveFAX("PJSIP/Avaya-00001788", "fax-20250217-134335.tif,f") in new stack
-- Channel 'PJSIP/Avaya-00001788' receiving FAX 'fax-20250217-134335.tif'

[Feb 17 13:43:35] ERROR[742556][C-00001784]: res_fax.c:1177 fax_session_reserve: Could not locate a FAX technology module with capabilities (RECEIVE)
[Feb 17 13:43:35] ERROR[742556][C-00001784]: res_fax.c:2226 receivefax_exec: Unable to reserve FAX session.
== Spawn extension (from-avaya, 5577, 2) exited non-zero on ‘PJSIP/Avaya-00001788’

I feel like I’m missing a fundamental piece here… I think I’ve ensured chan_pjsip, all the res_pjsip_* modules(except stir and geolocation), and res_fax are compiled in… and my dialplan is simply trying ReceiveFAX(filename,flags).

[jcolp]

It sounds like you don’t have res_fax_spandsp loaded.

[rcarsey1]

Indeed, that seems to be the culprit. I had gotten lost in the documentation from prehistoric Asterisk days. Seems I needed to install libtiff and spandsp libraries, then ./configure; make; make install asterisk again.