DTMF (Dual-Tone Multi-Frequency signaling) - MDN Web Docs Glossary: Definitions of Web-related terms
frequently referred to in the united states as "touch tone" (after the touch-tone trademark used when the transition from pulse dialing to dtmf began), dtmf makes it possible to signal the digits 0-9 as well as the letters "a" through "d" and the symbols "#" and "*".
... computers may make use of dtmf when dialing a modem, or when sending commands to a menu system for teleconferencing or other purposes.
... learn moreedit general knowledge dual-tone multi-frequency signaling on wikipedia pulse dialing on wikipedia ...

Using DTMF with WebRTC - Web APIs
dialing once the connection is open our design requires that when the connection is established, we immediately send the dtmf string.
...when you click the "dial" button, you should see a series of logging messages output, then the dialing will begin.

WebRTC API - Web APIs
webrtc concepts and usage webrtc serves multiple purposes; together with the media capture and streams api, they provide powerful multimedia capabilities to the web, including support for audio and video conferencing, file exchange, screen sharing, identity management, and interfacing with legacy telephone systems including support for sending dtmf (touch-tone dialing) signals.
...they're primarily used to send tone dialing sounds—or packets representing those tones—across the network to the remote peer.

Index - MDN Web Docs Glossary: Definitions of Web-related terms
frequently referred to in the united states as "touch tone" (after the touch-tone trademark used when the transition from pulse dialing to dtmf began), dtmf makes it possible to signal the digits 0-9 as well as the letters "a" through "d" and the symbols "#" and "*".

nsIRadioInterfaceLayer
speakerenabled bool constants call state constants constant value description call_state_unknown 0 call_state_dialing 1 call_state_alerting 2 call_state_busy 3 call_state_connecting 4 call_state_connected 5 call_state_holding 6 call_state_held 7 call_state_resuming 8 call_state_disconnecting 9 call_state_disconnected 10 call_state_incoming 11 datacall_state_unknown 0 datacall_state_connecting 1 datacall_state_connected 2 datacall_state_disconnecting 3 da...

Key Values - Web APIs
initiates voice dialing.

RTCDTMFSender.toneBuffer - Web APIs
the comma (",") this character instructs the dialing process to pause for two seconds before sending the next character in the buffer.

RTCDTMFToneChangeEvent.RTCDTMFToneChangeEvent() - Web APIs
the comma (",") this character instructs the dialing process to pause for two seconds before sending the next character in the buffer.

Event reference
adeneeded versionchange script events afterscriptexecute beforescriptexecute menu events dommenuitemactive dommenuiteminactive window events close popup events popuphidden popuphiding popupshowing popupshown tab events visibilitychange battery events chargingchange chargingtimechange dischargingtimechange levelchange call events alerting busy callschanged cfstatechange connecting dialing disconnected disconnecting error held, holding incoming resuming statechange voicechange sensor events compassneedscalibration devicemotion deviceorientation orientationchange smartcard events icccardlockerror iccinfochange smartcard-insert smartcard-remove stkcommand stksessionend cardstatechange sms and ussd events delivered received sent ussdreceived frame events mozbrowserclose mozbro...