DTMF stands for Dual-Tone Multi-Frequency.
DTMF is the signaling system used by touch-tone telephones, where pressing a key generates a unique combination of two audio frequencies. These tones are used for dialing, navigating IVR (Interactive Voice Response) menus, and inputting numeric data.
DTMF in WebRTC
WebRTC supports sending DTMF tones through the RTCDTMFSender API. This is essential for interoperability with the PSTN and traditional telephony systems, allowing WebRTC users to:
- Navigate phone menus (“Press 1 for sales…”)
- Enter conference PINs
- Interact with voicemail systems
In WebRTC, DTMF tones are not sent as actual audio frequencies in the media stream. Instead, they are transmitted as RFC 4733 telephone events within the RTP stream, which provides more reliable delivery. The receiving gateway converts these events back to audio tones if needed for the PSTN side.
