The engineers had also envisioned phones being used to access computers, and surveyed a number of companies to see what they would need for this role. With the widespread introduction of computers and bank machines, the phone keyboard has become "oddball", causing mistakes.
In retrospect, many people consider that this was a mistake.
The adding-machine layout, with 1 in the lower-left was also tried, but at that time few people used adding machines, and having the 1 at the "start" (in European language reading order) led to fewer typing errors. After testing 18 different layouts, they eventually chose the one familiar to us today, with 1 in the upper-left and 0 at the bottom. The Touch Tone system also introduced a standardized keyboard layout. Various tests of the system occurred throughout the 1960s where DTMF became known as Touch Tone. In this case pulse dialing made no sense at any point in the circuit, and plans were made to roll DTMF out to end users as soon as possible. It was clear even in the late 1950s when DTMF was being developed that the future of switching lay in electronic switches, as opposed to the mechanical crossbar systems then in use. This idea of using the existing network for signaling as well as the message is known as in-band signaling. It was as if you were connected directly to that end office, yet the signaling would work over any sort of link. At the remote site another encoder/decoder would decode the tones and turn out a series of clicks. Encoder/decoders were added at the end offices that would convert the standard pulse dialing clicks into DTMF tones and play them down the line to the remote end office. This was useful only as far as the local end office where the wires stopped, requiring operator intervention for long distance dialing.ĭTMF was developed at Bell Labs in order to allow dialing signals to dial long-distance numbers, potentially over non-wire links such as microwave links or satellites. The clicks were actually the connection of the calling party's phone line being made and broken, like flicking a light switch on and off. Prior to DTMF the phone systems had used a series of clicks on the phone line to dial numbers, a system known as pulse dialing. See: blue box for more details on the switching tones. The trunk signalling tones were different from the tones known as touch tone with a triangular matrix being used rather than a square matrix. Today DTMF is used for most call setup to the telephone exchange, at least in the Western world, and trunk signalling is now done out of band using the SS7 signaling system. DTMF is an example of a multi-frequency shift keying ( MFSK) system. (Redirected from Dual tone multi frequency)ĭual-tone multi-frequency ( DTMF), also known as Touch Tone is used for telephone signaling over the line in the voice frequency band to the call switching center.
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