Analog Fax with 3cx and Patton SN4114 via voip provider

[mikegillespie]

Hi,

I have a Fax connected to a SN4114 FXS.
The voip provider is Voicemeup.

A call placed to the fax connects but "fax tones" never take place and the connection times out. Similarly, this happens on outbound calls.

If i call the fax from a phone registered to 3cx, the fax will establish.

Any ideas?

Thanks

Mike

 

[leejor]

Your provider must support Fax.
Is the 4114 setup as a 3CX fax extension and on the same network as the 3Cx server (not hosted)?
Is everything correctly set to use T.38?

 

[mikegillespie]

Thanks Leejor,
The 4114 is configured using t.38 as setup in the FXS gateway provisioning file generated by the 3CX.
I have a ticket open with the provider on the t.38 issue as well.

 

[leejor]

You may want to make use of Wireshark to see how an external, and internal call differ. That might point to what may need to be changed.
It is puzzling that on an external call, you say you don't hear fax tones. What should be happening, is the fax machine answering, an attempted "handshake" to determine the speed, send caller ID, etc., and at that point, if the call cannot be established, it will drop. So, even if a fax call cannot be set up, for whatever reason, there should still be fax tones heard.

 

[eddv123]

If this is still causing you an issue please check and confirm the following:

* Firmware version and location of the Patton (location is very important as well as method of connection).

FAX over IP is very sensitive to delay so location and conversions (whether they are LAN/WAN or signalling IP >> PSTN) need to be kept to a minimum.

* As mentioned already T.38 support from the provider (however you can always switch from this and use G711 pass-through if not) this method (fax-pass-through) is where the T. 30 fax call is carried in a VoIP call encoded audio format.

* Baud rate of the FAX machine - if not already set you fax machine's transmission speed (BAUD rate) to 9600 bits per second (bps) or even slower to 7200 bps. This will increase the probability that all of the data will make it to its destination.

* Codec in use on the 3CX side and supported by the provider.

Failing all the above, why not simply Wireshark from the 3CX and send over the output, you can see all the relevant signalling and tone conversion in a PCAP trace - if your provider does not support anything you will see something like the below when the INVITE is sent: