Fax Extension behind SBC?

[jbryant84]

Has anyone had any success doing this? Inbound calls work fine. Outbound calls have no audio in or out. Found this out today trying to configure a fax adapter at a client site. Fax adapter is configured as usual, with the exception of using an outbound proxy of the SBC IP address. Have tried using 3CX server LAN IP or FQDN for registration, no difference.
For the purposes of a demonstration I configured a 2 port Cisco SPA112 analog adapter (officially unsupported by 3CX, but have had success using with other clients) with two extensions, Line 1 being a Fax extension, Line 2 being a regular 3CX extension, both using the SBC for an outbound proxy. I'm using a dumb analog phone for the purposes of the test, calling the same number. Note that there are zero packets/bytes received on the fax extension. Does anyone have any tips on a fix for this?

 

[jbryant84]

Nobody? Just looking to see if anyone has had any success using a fax extension across the SBC

 

[sip.bg]

Use a VPN instead.
You can build it very cost effective using MikroTik routers.

 

[jbryant84]

Typically we do using pfSense devices. Unfortunately this solution isn't usable for all clients for <reasons>

 

[sip.bg]

Typically we do using pfSense devices. Unfortunately this solution isn't usable for all clients for <reasons>

Ok, make a VPN with pfsense or whatever else devices you prefer. Allowing fax through pfsense firewall could be a challenge.

Keep in mind that fax is very sensitive to jitter, latency, packet loss, etc. Also SPA-112 is not the best choice for fax ATA. T.38 operation is not reliable enough in SPA-112, but this may be generally improved with new 3CX v15.5 sp1 functionality - fallback to G.711, needs to be activated manually and tested (beta feature).


Mikrotik cost starts from US $20, that's why I've recommended, plus I have many implementations, including remote faxes.

Regarding fax ata behind SBC, it depends on implementation of SBC, I haven't come across any confirmation it works or not with 3CX SBC. Maybe somebody from 3CX could answer this question.