DTMF Origins - The Fortuitous Mistake
DTMF DTMF was designed to provide address signaling to CO in PSTN at start of call Speed user address input (rotary dial was slow) DTMF originally turned off during conversation part of call Left on during call because of tip-ring polarity administration issues DTMF Origins Created simple, universal user input mechanism for all devices on the PSTN network end-to-end signaling standard across all PSTN terminal devices uPSTN service and application vendors discovered DTMF availability during call in late 70s & began using DTMF for application control DTMF Usage Today Virtually all PSTN terminals today have a standard 12-key keypad as a minimum DTMF for Address signaling is ubiquitous Universal User Input mechanism - DTMF has become the standard user input mechanism for all types of PSTN voice terminals to interact with services and applications