Verify that T38 is being used for faxes?

I’m new to this whole PBX thing and we are having a tough time getting faxing on our PBX to be reliable. I know our carrier supports t38, but how can I verify that it is being used?

Or, should be using something else than freepbx for faxing?

We currently have AsteriskNOW with FreePBX 2.8.0.4 and Asterisk 1.6.2.15.

You can use a hub to sniff the packets transmitted, with wireshark you can see if the packets are T.38 or ulaw

in the cli :

fax show stats

fax show capabilities

fax show settings

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