DTMF Digits Sent — VoIP DTMF Testing Metric
Track the number of DTMF digits sent per endpoint during IVR and telephony scenario testing. Essential for verifying DTMF delivery in automated call flows.
DTMF Digits Sent
| Property | Value |
|---|---|
| Key | dtmf_digits_sent |
| Unit | Count |
| Type | Cumulative counter |
| Direction | Send |
| RFC | RFC 4733 (RTP telephone-event), RFC 2976 (SIP INFO) |
What It Measures
DTMF Digits Sent counts the total number of DTMF (Dual-Tone Multi-Frequency) digits transmitted by an endpoint during a call. Each digit (0-9, *, #, A-D) increments the counter by one, regardless of whether the digit was sent via RTP telephone-event (RFC 4733) or SIP INFO method.
This metric is the primary indicator for IVR scenario testing — it tells you whether your test endpoint successfully generated the DTMF sequence your scenario required.
Why It Matters
IVR systems, voicemail access codes, conference PINs, and call center menu navigation all depend on reliable DTMF delivery. If digits are not sent, the call flow breaks — the IVR never receives input, the conference bridge never unlocks, the caller loops forever in a menu.
During load testing, DTMF delivery can degrade under congestion. Digits may be delayed, truncated, or silently dropped. This metric lets you verify that every digit in your scenario was actually transmitted from the endpoint.
How CallMeter Measures It
CallMeter counts DTMF events at the source, immediately after generation. For RFC 4733 (RTP telephone-event), each named event packet with a new event ID increments the counter. For SIP INFO, each INFO request containing a DTMF payload increments the counter.
The count is cumulative for the call duration and reported per second alongside all other metrics.
Thresholds
Thresholds depend on your test scenario. Compare the sent count against the expected digit sequence length:
| Condition | Meaning |
|---|---|
| Sent = Expected | All DTMF digits were generated successfully |
| Sent < Expected | Some digits were not sent — scenario may have stalled or timed out |
| Sent > Expected | Unexpected — possible duplicate events or scenario loop |
How to Fix It
- Check the scenario definition. Verify the DTMF action in your test scenario specifies the correct digit string and timing.
- Check the DTMF method. If the remote system expects RFC 4733 but your test sends SIP INFO (or vice versa), digits may be ignored by the receiver. See DTMF Method.
- Check call state. DTMF can only be sent during an active call. If the call setup failed or ended early, DTMF digits will not be generated.
- Review timing. If digits are sent too early (before the IVR prompt plays) or too fast (inter-digit interval too short), the remote system may miss them.
Related Metrics
- DTMF Digits Received — Confirms the remote side received the digits
- DTMF Method — Which transport was used (RFC 4733 RTP or SIP INFO)
- Call Duration — Verify the call lasted long enough for the full DTMF sequence
- Scenario Actions Executed — Overall scenario step completion