Can't get faxes to work with voipfone as trunk provider

[Stulander]

• I'm using Voipfone as a SIP trunk provider. (I know they're not officially supported.)
  • Voipfone DO support T.38
• I have a Grandsteam HT801 connected to an old Brother 1020 Plus fax machine.
• I have read the following guide: https://www.3cx.com/voip-gateways/grandstream-ht-fxs/
• I have two numbers associated with my voipfone account (one for calls, one for fax)
• For the SIP trunk, I have two DIDs - the aforementioned numbers

• Under inbound rules, I have one rule for inbound calls (which works fine) and one rule for inbound fax (which does not)

• I've set up the HT801 under Advanced>FXS/DECT, and assigned an extension.
  • This seems to be working, I can call the fax machine and make calls from it.
• I've tried G711 and T.38 transmission mode

Sending a fax to the fax number (above photo) ignores the Fax inbound rule, and uses the "Inbound calls" one instead - Rings extension 000. If I pick up the extension, I just hear a beep every few seconds.

• I've also tried using the built-in fax server, but with the same issue. Calls just go straight to 000, as per the picture above.

We've been using voipfone with 3CX for almost a year without issue, I'm just now trying to add fax and not having much success. What might the issue be?

Thanks

 

[leejor]

Do other DID rules, from the same provider work correctly?
If you modify the destination, of the Fax rule, to a "normal"' extension, does it work?

It may be that the number in the DID rule you have created, does not match the incoming DID number exactly, or perhaps a DID number is not being sent. Check the 3CX Activity Log to see if that is the case, or use wildcards (*) at the beginning of the rule number to compensate for any unexpected prefixes added by your provider.

 

[cobaltit]

Whoops. Read too fast. Thought you had two trunks and not two DIDs on the same trunk.

I'd read this:

https://www.3cx.com/docs/source-identification-issues/

 

[Stulander]

Update: After speaking to voipfone again, they said that T.38 is supported, but only when buying a "fax number" specifically, and when you do that you can only do fax-to-email using their service. Apparently T.38 does not work with a standard VOIP SIP trunk.

I'm not entirely sure why they told me that T.38 is supported in that case. The guy I spoke to yesterday asked if I had tried to send a fax to the voice number, which suggests it should work.

Here's an excerpt from the chat I had today:

Support 09:08
You will need a fax number on the account to be able to receive a fax and the fax will then be sent to you via email. T.38 is supported

Me 09:09
Is it possible with voipfone to have the T.38 fax recieved by an on-site PBX?

Support 09:11
At the moment the fax can only be routed to email, no other routing is available currently as our fax service is very basic, I will however send your request over to our developers to get them to take a look at this for you

Me 09:11
ah ok, so I take it t.38 isn't supported with a standard number

Support 09:12
Not with a standard voice number

I imagine nothing will happen - if I were a developer I'd probably roll my eyes at such a request. Personally I am more than happy with fax to email, it's just a weird request from management that we're able to use a physical machine.

I guess I will just use a PTSN line and hopefully by the time analog is shut off nobody on the planet is still using fax.

 

[cobaltit]

So this is pretty common. Many SIP trunking providers (ourselves included) do this for many reasons. Sometimes it's because we have multiple carriers and some work better than others for delivering T.38 so we want to make sure the number is with the carrier that provides the best T.38 experience. Other times is because they have dedicate infrastructure for handling T.38 so things need to be configured differently as far as how the call routes through their network or how they hand it off to you. You'll see that in many provider portals when buying new numbers. They will have ones flagged as T.38 or fax capable. Same thing when porting in numbers, you will often be asked if a number will be used for fax.