ATA won't connect on UDP

[sip.bg]

So personally we only offer FoIP to clients we don't like and with a big disclaimer that we don't support it. We recommend all customers that actually care about faxing keep a POTS line for outbound faxing and we use 3CX built-in fax server for inbound. Other solutions are using the same provider handling PBX dialtone and routing the fax number to a 2nd trunk registered directly to the ATA. If you really want reliable FoIP then you go AudioCodes HTTPS faxing but that will most likely require a second provider.

Well, I generally agree with your approach, it's safe enough.

In reality FoIP depends too much on provider, internet, adapter itself (most adapters are not supporting T.38 enough reliably). The issue with providers is mostly falling back to G.711 (T.30) and vice-versa to T.38. Officially supported providers by 3CX are expected to support T.38 fax also.


We have several customers, including ourselves, using fax remotely via VPN with AudioCodes Mediant adapters and this works stable enough -- may be even better than analog lines (POTS) and many customers with local adapters (same local network with the PBX).

What I say from my experience is AudioCodes Mediant is handling T.38 properly. Not the case with most other brands.
3CX PBX itself is transparent for T.38 to adapter. In the case where you receive fax to email, T.38 is terminated by 3CX.


Other very stable combination is latest Asterisk releases (FreePBX 13, etc.) where T.38 is terminated into PBX itself and adapter is connected via G.711 (T.30), not T.38 or fallback is supported. This works with almost any adapter you attach with the default settings of FreePBX.

I haven't tested G.711 fallback in 3CX v15.5 -- should be enabled manually, as it is still beta, may improve reliability.


As a summary: If you provider is supporting T.38 good enough and you use an adapter like AudioCodes Mediant, you should be lucky fax user both in local and remote offices (via VPN). Otherwise try a fax-to-mail and mail-to-fax service offered by some providers, they work usually well.

I will send you a sample Mediant config file, if you go for it.