Fax over IP failure with 3CX Sip server 407 and 488 Errors

[shinto]

Hi 3CX team,

I am using 3cx version 16, as SIP server for our Fax over IP Communication.
Currently facing “407 Proxy authentication required” and “488 Not acceptable here” errors while trying T.38 Fax. Both Error codes are sent from the 3CX Sip Server.
Please find attached Wire shark and 3cx Activity logs.
Please have a look and share your inputs on how to resolve this issues. 488 Error code is resulting in a Disconnection. Not Able to under stand why the T38 Reinvite is Not acceptable for the 3cX server.
In below snap,
IP 192.168.11.20 corresponds to 3CX SIP server.
192.168.11.21 - Fax Sender
192.168.11.22 - Fax Receiver



Thanks,
Shinto

 

[YiannisH_3CX]

Are you using a Fax extension or a regular extension for your ATA device? What ATA device are you using and how did you set it up?

 

[shinto]

We are using a Fax Extention. We don't use any ATA device,
We use fax devices capable of doing IPFax at sender and receiver side. We have configured SIP server settings to the 3CX IP at both sender and Receiver devices (both IPFax capable).
The same setup works with SIP servers other than 3CX. We are actively trying now with 3CX, please share your inputs to fix this.

 

[YiannisH_3CX]

I am not sure I can help with this since its a configuration we have never tested. I would test receiving a FAX to our FAX server directly to see if that works first.
If it does then I would recommend using a supported ATA device to connect your Fax machines for outbound faxing.

 

[shinto]

Thanks for the input, I will try with a ATA device and update.