Second fax call NOT getting busy signal with commercial fax module

When one fax machine dials in, the system answers it and starts receiving the fax. While this is happening, if a second incoming fax dials the same fax number, it will go to the SIP failover number (my cell number). I would expect the second fax machine to get a busy signal, then it would wait and call back later. But that is not what is happening. Do I have someone on the commercial fax module set wrong? On Settings->Fax Configuration, there is not many parameters to set.

My system is:
Asterisk 11.2.1
Commercial Fax module
Phonepower SIP provider

Why would you expect that? As far as the system is concerned, the second call “could be” a voice call, or whatever. The FAX determination is done after the call is picked up. Since the first line is in use, the call is routed to your second choice line, which is your cell phone.

Sounds like you need to set up a ring group for all of your inbound FAX numbers with a failover to a “Terminate Call - Busy” instead.

Commercial FAX module is all about sending faxes, not receiving them.

Because this is a dedicated fax DID. Your ring group suggestion should work perfect for what I am trying to do. Thank you.

As a rule with SIP-based PBX systems (especially Asterisk based solutions), the system is designed to always get the call somewhere. The idea of a DID being dedicated is more by fiat then by design. Once the system gets it, it will always try to send the call somewhere. Unless you specify that the “failure” destination for that inbound route is “Hang Up - Busy”, the system will always try every possible destination before it fails, and even then might not end up with a busy signal.