Faxing with PRI and FXS, NO SIP USED - Your thoughs please


I am contemplating migrating all our phones over from a legacy PBX to a Asterisk-based installation. There are three fax machines currently used daily through the legacy PBX, which is fed by an ISDN30 line.

My current thoughts were to a Digium or Sangoma PRI card to manage all incoming calls, forwarding all voice calls to their relevant SIP extensions based on DDI’s. If a call is incoming with a fax DDI the idea is to route that via a seperate Digium analogue card, e.g. TDM400P with three FXS modules, which in turn are connected to the fax machines.

Does this sound like a reasonable and more importantly reliable solution?

Any thoughts are appreciated :smile:

Dear subliminal,
I have multiple install with at least one fax machine fed from TDM400Ps with S110M modules. Calls come in over a PRI line to TE110P. DID numbers bridge the call in the dialplan to the TMD400P board. This has worked perfectly well for me many times. I have always used digium cards and really not had too many complaints.

Good luck. :smile:
-Cheers, Peter.

I have a full T interfaced to a digium card, and route calls over to a digium analog card to feed the fax, alarm, and a modem. It works perfectly. I have a line like…

exten => 478#######,1,Dial(Zap/25)

to match the DID & route over to an analog channel

pbrunnen & puckett_jw,

Thank you so much for your replies - its a big help to know that it has been tried before and found to work :smile: I’ll let you know how it works out!

Thanks again,



I have the same setup but am having issues with noise coming across the analog lines to the fax machine and modem data connections. Can you give me insight to what your configuration setup is like? I am thinking it has something to do with my timing issues, but am not positive. Below is my diagram setup. Thanks for the help in advance.

PSTN–>A102–>ASTERISK–>TDM2400P(fxs lines)–>Modem/Fax


Can you please some some specs about your configuration. Like the zaptel.conf & zapata.conf files. I am assuming that box these cards are in the same asterisk box? You say “PSTN” to the A102, but I am also assuming that is a T1 or E1. Have you checked the simple things, like that the wire into the TDM is clean? Can you plug an analog headset into the closest point to the TDM to see if you hear static?

We have been able to reliably fax through a PRI and analogue Sangoma card using a timing cable as described in wiki.sangoma.com/t1e1analogfaxing. Perhaps there is something similar possible with the Digium H/W?

just make sure you disable all echo cancellers on the fax calls and using digium cards you should be fine this way,