Key Press or DTMF Not Working

• 02 August 2022
• IP PBX,VOIP
• Written by George Dockrell

IVR choices do not function when keys are pressed, or, more precisely, DTMF signaling is not functional on your incoming calls. Once callers reach your main number, they cannot reach an extension they dial. They press the key(s) to reach an extension, but it reaches nowhere. When VOIP systems are put up, this problem is typical. The DTMF signaling is not recognized by your IP PBX server, which is the cause of this.

What is DTMF?

DTMF is not a native signaling format for Voice over IP(VoIP) systems. Session Initiation Protocol (SIP) is a signaling and dialing protocol used by VoIP systems. Most VoIP systems additionally feature DTMF capacity through control trunk lines or, for example, dial-in systems to interface with older systems and for widespread compatibility. If a lossless encoder is utilized, they could also support DTMF on the inbound stream.

How to Activate DTMF on VOIP Software Such as Asterisk or Issabel or FreePBX?

Your IP PBX server must support DTMF. Callers won’t be able to access IVR choices if DTMF isn’t enabled in your IP PBX server. Verify that ulaw, alaw, and gsm are all enabled in your SIP settings.

Here is a working example of SIP trunk settings with DTMF enabled:

type=friend

secret=Your Password

insecure=very

host=Your PBX Server IP or hostname

dtmfmode=auto

dtmf=auto

nat=yes

qualify=yes

canreinvite=no

relaxdtmf=yes

context=from-trunk

disallow=all

allow=ulaw & alaw & gsm