DTMF Not Working

What Causes This Error

DTMF tones (keypad presses) are not being detected or transmitted correctly. Agents pressing keys during IVR navigation or transfer scenarios have no effect. Caused by DTMF mode mismatch between VICIdial/Asterisk and the carrier (RFC2833 vs. SIP INFO vs. in-band), codec transcoding issues (G.729 drops DTMF), or NAT issues with RTP DTMF packets.

How to Fix It

• 1 Check current DTMF mode in sip.conf: grep dtmfmode /etc/asterisk/sip.conf

• 2 Set to RFC2833 (most compatible with carriers): dtmfmode=rfc2833

• 3 If using G.729, switch to ulaw/alaw to preserve in-band DTMF

• 4 Check carrier DTMF requirements (contact carrier support)

• 5 Test DTMF detection: dial into test IVR and verify key presses register

• Enable DTMF debug: asterisk -rx ‘core set verbose 5’ then press keys in active call

• 7 If using SIP INFO: dtmfmode=info in sip.conf for that peer

How to Prevent It

Document DTMF mode requirements for each carrier and configure correctly at setup. Test DTMF during initial carrier integration. Avoid G.729 codec if DTMF relay is needed for IVR interaction.

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