No dtmf after transfer to external number

[Michael Groom]

We have all calls going to ivr. A caller can then choose an option and dtmf works. One of the options is to transfer to external number using a dummy extension. That works jsut fine. The problem is when the external number answers( which also happens to be an ivr) dtmf no longer works properly. We get “ sorry that extension is invalid” from their pbx. Dtmf works just fine if we call this external number from our phones. Just not when its transfered from our ivr.

 

[cobaltit]

Does your system pass the firewall checker?

 

[YiannisH_3CX]

Hello @Michael Groom

How is the Dummy extension setup? Do you have the option "Ring my mobile simultaneously" enabled?

 

[Michael Groom]

No ring my mobile simultaneously is unchecked I have it set up to forward to mobile win busier run register and I’ve got the Number we need to call in the mobile field of the extension. The call works just fine just no DTMF when the call is placed. Also we did not worry about the firewall check her since the VIP gateway is on the same subnet as the phone system due to it being at Edgemark from Cox so it comes in his pure sip on our network

 

[leejor]

I have to assume that the original caller is sending audio DTMF, which may, or may not be converted at some point to SIP messaging,and then perhaps back to audio, to be passed on through the outgoing trunk. If it remains as audio, it may be that the level is too low to be detected reliably by the far end IVR.

What you might do, to see if DTMF gets through at all, and to check the quality. Forward to another outside number, that you can answer. When the caller (presumably someone you have place a test call) sends DTMF, you can then check to see if it gets through, and what it sounds like. There may also be an issue with the far end IVR and it's ability to detect DTMF tones below a certain threshold. There are also a DTMF test numbers available that you could forward the call to. https://thetestcall.blogspot.com/

 

[Michael Groom]

Thanks I will try this. I also noticed when the 3CX transfers the call it transfers it as a supervisor transfer and never releases the call due to the fact I’m assuming that you’re transferring to an internal extension that’s forwarded this could be the problem where as any other PBX would release the call therefore allowing natural DTMF to flow and not being converted by the 3CX in someway. I’m not 100% sure but I believe that those two are correlated.

 

[Michael Groom]

Going to open a ticket with support as well as this feature has to work for the client it worked with their old IVR and their old PBX and they’re wondering why it won’t work with this one

 

[leejor]

You don't say if the incoming and outgoing trunks are VoIP, a gateway, or a combination. If a gateways is involved, then there may be some DTMF Method options that can be changed and tested. Audio levels can also be tweaked, if needed. There may also be an unforeseen be an issue with your provider in how they are handling DTMF. A number of variables.

 

[Michael Groom]

Inbound and outbound are handled by voip via cox. They put their equipment onsite so our connection to the provider is a local lan address. Also DTMF works normally inbound and outbound. The problem only occurs when a call is transfered. I also tried manually transferring a call to this external number and the dtmf didnt work correctly.

 

[Michael Groom]

So using https://thetestcall.blogspot.com/ to test a call it is seeing my dtmf as duplicates so if i press 7 it plays back to me 77

 

[leejor]

What i suspect is happening...

The audio DTMF, at some point is being converted to a SIP message, then being reproduced further along. The original audio DTMF is also being passed on, resulting in tones being sent twice.

 

[Michael Groom]

That make perfect sense now hopefully 3cx can find out where this is happening in the system and they have a fix for it. Thank you for your help.

 

[Michael Groom]

So i believe what is happening here isthat The DTMF comes in from the first call. Then the system makes a second call out based on forwarding rules. This call is using a new line hence new dtmf Since the phone system does not release the call once the transfer has been made there are still 2 active calls hence 2 DTMF tones being registered when a button is pressed. So if 3cx can not connect the 2 sip calls together and then release supervision then this wont ever work.

 

[leejor]

Rather than use forward, perhaps try using the "ring my mobile at the same time" option, see if there is a difference in behaviour. When using a dummy extension (unregistered), this may require that you create an extension application using PUSH. This way even if there is no physical set registered, because of the PUSH option, 3CX will assume there is a "phone" there and also send the call to the "mobile" number.

 

[Michael Groom]

Wow leejor this fixed the issue. you are a genius. I never would have even tried doing that because i have seen dtmf issues caused by that being enabled in other instances.

 

[leejor]

Glad it worked for you. The method you were using should, (in theory) work, so there is something else going on.

 

[YiannisH_3CX]

Glad to see you found a solution to your issue however your original scenario should also work. I have tried replicating it with a couple of providers and the PBX only sends one DTMF to the second IVR. If you can create a ticket regarding this with our support department please do so as they will need to go through the call flow to determine the cause of the issue.