Why do "FAX Extensions" exist? Difference to normal extensions?

[nobody]

I have mixed success sending faxes using Cisco and other adaptors. I think it does not make much difference if they are configured as a normal extension or a "FAX Extension" in 3CX.
What ist the difference between normal and FAX?
Should I always use a FAX extension, and what are the benefits?

Besides of the Howto which tells I should use the FAX Extension when connecting a FAX machine, I did not find much more detailed information.

TIA

 

[eddv123]

I don't think there is that much difference (unless a 3CX representative can confirm) as all the FAX related settings (such as mode settings T.38/G.711 Pass-through) are saved in the FXS Gateway settings not the extension(s) themselves.

Although when you add a FAX extension they do reside in the "System Extensions" of the PBX - that is the main difference.

FoIP can sometimes be a challenge to setup so would always recommend using supported devices and in a supported environment (hosted systems via VPN only).

 

[leejor]

There are restrictions on Fax extensions, where you can, and can't use them. I'm sure that part of that is to increase that chance of it working, and avoid the frustration when it doesn't. It probably cuts down on the number of trouble tickets from people that don't understand how Fax over VoIP actually works. There is also a tie-in with the 3CX Fax to PDF service.
https://www.3cx.com/docs/manual/fax-server/

 

[nobody]

The only thing that made a difference I found out recently was, that if after I checked "pbx delivers audio" the success rate increased at two of three locations. I did not expect this, because audio will have to go through another hop (If my understanding is correct: pbx delivers audio unchecked: UDP data will go direct from the ATA adapter to the internet, if checked UDP will be relayed by the PBX).

 

[eddv123]

Basically yes, on a standard SIP call the SIP protocol will setup a call with the assistance of the PBX.

One negotiation has taken place audio then passes between the endpoints directly. Enabling the setting however causes the audio stream via the PBX not point to point.

As standard this setting is used for remote extensions using STUN and when call recording.

 

[leejor]

As standard this setting is used for remote extensions using STUN and when call recording.

While it can help fix no audio issues, for sets are using STUN (usually multiple sets at one location), I would not use it by default, only if necessary.

 

[eddv123]

As per slide 10 here: https://www.3cx.com/3cxacademy/videos/intermediate/configuring-remote-extensions/

I have had to enable this when using multiple phones via VPN also, where in theory you should not require this.

 

[StefanW]

there is a difference and specially when you use voip provider. Re-Invite is commonly disabled in trunk as the TDM network is not there to manage you music on hold (MOH). So when an internal ext. presses "hold" then 3CX does not send to the provider a hold request but starts sending your MOH (and in this way you can control what MOH should be played).

However FAX need to switch codecs which is also made via Re-Invite. Here is the difference, those fax extension are allowed to do so, even the capability is been disabled in the trunk...