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DTMF Tones & 3cx - - 06-30-2015 11:19 PM

I have been having an issue sometimes where our phone system will not send out the correct DTMF tones. For example, if I call into a company and have to dial an extension, or call into a conf call and have to hit the conf call ID, it will skip/miss digits that I enter. This seems to be random, but a few companies we work with a lot have the same issue, so it is very annoying.

I am running T48 and T38 phones on 3cx 12.5. All phone have the same issue. I have attached snap shots of the transmission from wire shark. It appears that the DTMF signal is being sent 3 times for each 1 time I hit the button. When I call my cell phone and hit a button the DTMF tone come over all garbled and stutters.

T48 Firmware
T38 Firmware

Thanks in advance.

RE: DTMF Tones & 3cx - tsukraw - 07-01-2015 01:10 PM

I've worked on many DTMF issues over the couple years using these phones and 3CX. Most of the time it is actually not the phones.

What time of connection do you have to the outside world?
SIP Trunk?
Also what kind of hardware are you using to connect to the outside?

So looking at your captures it is normal to see the DTMF sent 3 times for each digit. It is how it works.

Depending on which type of connection you have to the outside world we would wnat to see a capture from that device. That way we could see what 3CX is sending since the traffic in the captures you provided is from the phone those to me look clean.

If you could please post the full wireshark file so i can have a look. If you dont feel comfortable posting PM me the log.


RE: DTMF Tones & 3cx - Timeinspain - 11-24-2015 12:42 AM

I have 5 new T48G phones also running on 3CX 12.5 with version installed on the phones. I have exactly the same problem. If I try to answer automated phones by pressing the keypad, it does not recognise the keys pressed. Anybody know what to do ?

RE: DTMF Tones & 3cx - James_Yealink - 11-24-2015 04:15 AM


Can you try changing the DTMF type under Account-> Advanced and check again.
If it doesn't work you can also try changing DTMF duration.

features.dtmf.duration =
It ranges from 0~300, default value is 100.