Analog fax connection to Asterisk

I need to connect a traditional analog fax to Asterisk.

I have Asterisk set up and it works well with 100 IP phones.
However, I am trying to use the LinkSys SPA-3102 (PAP2T) adapter to connect an old analog fax. But it does not work.

The internet line connection of the PAP2T goes to the Asterisk phone network, the Line 1 is connected to the fax machine.
When I call this phone number, it rings alright, but after 6 or so rings it says “Service Unavailable”.

A SIP trace on the phone shows that asterisk says “no answer” as reason for Hang-up. But it 's connected.

If anyone knows the how-to regarding fax connections please let me know urgently. What’s different in Asterisk as compared to a normal VoIP phone extension?


Peter Schulz

First you should decide on the fax mode you will use - T.38 vs G711 transparent.

T.38 is supported by SPA3102 but not by PAP2(T).
For T.38 you will need (at least) the following settings:

in sip.conf:

t38pt_udptl = yes

in sip.conf or users.conf, for fax extension and you VoIP provider:

t38pt_udptl = yes

If the fax machine connected to the ATA is not going to off-hook state on incoming call then this has no relation to Asterisk.

What kind of lines are you using ? In general I think faxing with asterisk works but there are issues and you may rip your hair out in the process. From what I have seen call weaver ( which is a fork of asterisk works a lot better with faxing (it has full T.38 support).