t38 fax

[alwtech]

I need to be able to add Grandstream HT801 and HT802 ATA's as remote devices to a cloud instance of 3cx. These are going to be added to become fax modules and use for fax.
The issue that I am having is that they will not provision outside the lan or through a SBC.
Is there anyway to add this to 3cx without being local or through a SBC?
or is there a way to add it to a ext and allow t38 passthrough.

 

[cobaltit]

So you're saying these instructions don't work?

https://www.3cx.com/voip-gateways/grandstream-ht-fxs/

But yes, you can absolutely provision any SIP compliant device manually to any 3CX instance whether local or cloud.

 

[alwtech]

That is correct, "o “Local LAN” or “3CX SBC”". The pbx is hosted on light sail and when I try to connect an ATA directly 3cx blocks the connection due to it coming from an address that is not local to the instance or a sbc.
I can manually configure the ata to connect to an ext but the t38 session fails on the re-invite. I am not sure if there is a way to make it do t38 passthrough or not. I have no issues with manually configuring the ATA to connect and pass voice traffic. The issue that I am running into is trying to make t38 work for fax.


My goal is to be able to deploy the ATA's and use them for faxing without having to also deploy a SBC to go with that setup.

 

[cobaltit]

Are you using a supported SIP trunking provider?

 

[alwtech]

Yes. Telnyx. But the issue is that I can’t get the ATA’s to connect in a direct stun type setup. If I run them locally to the pbx or through a sbc. I do not have this issue.

 

[cobaltit]

Hmm... well you might just want to make a separate trunk straight to the ATA then.

 

[alwtech]

That is what I have been doing Just looking for a better solution that I would have more control over. It would be nice to be able to run them though the instance for reporting purposes.

 

[YiannisH_3CX]

I can manually configure the ata to connect to an ext but the t38 session fails on the re-invite. I am not sure if there is a way to make it do t38 passthrough or not.

This is because you are using a normal extension which does not support T38 re-invites. You need to register a Fax extension to the device but it has to be local or SBC. Not sure why you do not go the SBC route. Fax through SIP is challenging to say the least. You do not want to be running an unsupported scenario as well. Setting up an SBC is easy and inexpensive so I would highly recommend going that route.