DTMF and iPhone with VAD

[SWSDEV]

We have an interesting problem.

We have an IVR on a hosted cloud server built with the VAD. It has worked great, except now we've found when anyone with an iPhone calls the IVR it does not respond to DTMF tones.

What could we possibly check?

 

[VAD_Support]

Well, this is generally a problem with the encoding of DMTF digits. There are several ways to send DTMF digits over VoIP. If digits are send in-band, they may be lost depending on the codec used. There is a good blog post about this here: http://www.3cx.com/blog/voip-howto/dtmf-rfc2833/

Something you can try is verifying if the softphone on the iphone is configured to send DTMF digits in-band. In that case, try changing that configuration to RFC2833 or SIP INFO.

 

[SWSDEV]

Is the end user really going to have control over that? This is a regular call from an iPhone and not a "softphone" installed on the iPhone.

Is this more a setting somewhere on the VAD to accept different types of tones? Has the VAD been tested with the different DTMF options?

 

[VAD_Support]

This is a setting that is configured in every SIP endpoint. Somewhere, the call from the iphone is converted from a regular phone call to a SIP call, and there you need a gateway that converts DTMF digits to the right signals in SIP / RTP.

The VAD can not be configured to accept or reject some DTMF method. It is the 3CX IVR which interprets digits and process them as requested by the VAD. The 3CX IVR understands any of the 3 methods (in-band on RTP, RFC2833 on RTP, and INFO on SIP). But if you are using a high compression codec, then in-band DTMF digits may be lost. If you for example use PCMA or PCMU, then in-band DTMF digits will very possibly arrive the 3CX IVR...

How does your 3CX server connect to regular phone lines to receive calls from an iphone? Do you have a VoIP gateway? How is it configured in regards to DTMF digits?

 

[SWSDEV]

It is connected to a Broadvox SIP Trunk. No gateways.

 

[SWSDEV]

I don't see the DTMF settings for the trunk

 

[VAD_Support]

I'm pretty sure that your Broadvox SIP trunk is sending DTMF digits in the right way. Are you receiving DTMF digits from other phones on these lines? Can you try a simple Digital Receptionist in 3CX in order to see if you can choose a menu option?

 

[SWSDEV]

Other DTMF settings seem to be working fine. I will do some troubleshooting to try to limit the possibilities for causes.

This is from the log though.

16:25:55.991 [MS211000] C:1.1: 209.249.3.60:34076 is delivering DTMF using RTP payload (RFC2833). In-Band DTMF tone detection is disabled for this call segment.

 

[VAD_Support]

The log says that the remote endpoint is sending DTMF digits using RFC2833 over RTP, and then disables in-band tones detection. That is because in-band tone detection consumes a lot of CPU, so when 3CX detects that digits are arriving as RTP payload, in-band detection is disabled for that call.

So, it seems that DTMF digits are being sent in the right way. Is that log from a call with an iphone?

 

[SWSDEV]

No, that was from a landline.

We checked with several iPhones, and at first the same problem was happening. But now it is no longer happening. I dont know why, maybe the server reboot, or when I was just adjusting the settings, but it's gone. It's a mystery this time.

 

[VAD_Support]

Good to know, let me know if it happens again...

 

[matictec]

We have tested a liitel bit with the VAD and have the same problem.

Here a short description:

The way it should be:

User Input -> Initial Prompt played -> Valid Input -> E-Mail sender component run also

It works, but after valid input the mail is send but the initial promt played again then call ends. in 3cx log i can see the dtmf warning. sometimes this also happens over our voip provider.

 

[VAD_Support]

Can you upload the 3CXIvrServer.log file and the project you're using? I would like to reproduce it here.
Thanks,