DTMF Digits Received — VoIP DTMF Verification Metric
Count DTMF digits received by an endpoint during IVR testing. Verify end-to-end DTMF delivery across your SIP infrastructure.
DTMF Digits Received
| Property | Value |
|---|---|
| Key | dtmf_digits_received |
| Unit | Count |
| Type | Cumulative counter |
| Direction | Receive |
| RFC | RFC 4733 (RTP telephone-event), RFC 2976 (SIP INFO) |
What It Measures
DTMF Digits Received counts the total number of DTMF digits an endpoint received during a call. This is the receive-side complement to DTMF Digits Sent and proves end-to-end DTMF delivery through your SIP infrastructure.
Why It Matters
Sending DTMF digits is only half the story. The digits must actually arrive at the receiver for the IVR flow to work. Network issues, transcoding gateways, SBCs that strip telephone-event payloads, or mismatched DTMF transport methods can all cause digits to be sent but never received.
Comparing sent vs. received DTMF counts across endpoints is the definitive test of DTMF reliability in your infrastructure. A mismatch means digits are being lost in transit — and your IVR, conference bridges, and voicemail systems are silently failing.
Thresholds
| Condition | Meaning |
|---|---|
| Received = Sent (remote) | All digits delivered end-to-end |
| Received < Sent (remote) | Digits lost in transit — investigate SBC, transcoding, or network path |
| Received = 0, Sent > 0 | Complete DTMF delivery failure — likely transport method mismatch |
How to Fix It
- Compare with DTMF Digits Sent on the remote endpoint. If sent > received, digits are being dropped between endpoints.
- Check SBC/gateway DTMF handling. Many SBCs perform DTMF interworking (RFC 4733 ↔ SIP INFO). If misconfigured, they may strip or misroute DTMF events.
- Verify payload type negotiation. Confirm both sides agreed on the telephone-event payload type in the SDP (typically PT 101).
- Check for transcoding. If media passes through a transcoder, DTMF events may be consumed and not forwarded.
Related Metrics
- DTMF Digits Sent — What was transmitted
- DTMF Method — Transport method used
- Packet Loss Rate — Network loss that may affect DTMF delivery