Dual-tone multi-frequency signaling

DTMFtouch-tonetouch tonedual-tone multi-frequencytone dialingtouch tonestouchtonephones work by hearing chords (a combination of one or more notes played at the same time) of sounds as numbersTouch-Tone dialingDTMF signals
Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.wikipedia
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Telephone

phonetelephonesLocal Telephone Service
Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.
Until the 1960s dials used almost exclusively the rotary technology, which was replaced by dual-tone multi-frequency signaling (DTMF) with pushbutton telephones (A4).

Push-button telephone

10- or 12-button touch-tone telephonespush-buttonpush-button dialing
DTMF was first developed in the Bell System in the United States, and became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963.
On 18 November 1963, after approximately three years of customer testing, the Bell System in the United States officially introduced dual-tone multi-frequency (DTMF) technology under its registered trademark Touch-Tone.

Telephone keypad

keypad12-key telephone keypaddial pad
The Touch-Tone system using a telephone keypad gradually replaced the use of rotary dial and has become the industry standard for landline and mobile service.
It was standardized when the dual-tone multi-frequency signaling (DTMF) system was developed in the Bell System in the United States in the 1960s that replaced rotary dialing originally developed in electromechanical switching systems.

Telephone exchange

exchangescentral officeexchange
Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.
At a later date many also accepted DTMF "touch tones" or other tone signaling systems.

Rotary dial

dialrotary telephonerotary phone
The Touch-Tone system using a telephone keypad gradually replaced the use of rotary dial and has become the industry standard for landline and mobile service. Prior to the development of DTMF, telephone numbers were dialed by users with a loop-disconnect (LD) signaling, more commonly known as pulse dialing (dial pulse, DP) in the U.S. It functions by interrupting the current in the local loop between the telephone exchange and the calling party's telephone at a precise rate with a switch in the telephone that is operated by the rotary dial as it spins back to its rest position after having been rotated to each desired number.
From the 1980s onward, the rotary dial was gradually supplanted by dual-tone multi-frequency push-button dialing, first introduced to the public at the 1962 World's Fair under the trade name "Touch-Tone".

Multi-frequency signaling

multi-frequencyMFmultifrequency
Other multi-frequency systems are used for internal signaling within the telephone network.
Multi-frequency signaling is a precursor of modern DTMF signaling (TouchTone), now used for subscriber signalling.

In-band signaling

in-bandin-band signallinginband
The earliest of these were for in-band signaling between switching centers, where long-distance telephone operators used a 16-digit keypad to input the next portion of the destination telephone number in order to contact the next downstream long-distance telephone operator.
When dialing from a land-line telephone, the telephone number is encoded and transmitted across the telephone line in form of dual-tone multi-frequency signaling (DTMF).

Signaling (telecommunications)

signalsignalingsignalling
Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.
An example is dual-tone multi-frequency signaling (DTMF), which is used on most telephone lines to customer premises.

Pulse dialing

dial pulsepulse diallingpulse dial
Prior to the development of DTMF, telephone numbers were dialed by users with a loop-disconnect (LD) signaling, more commonly known as pulse dialing (dial pulse, DP) in the U.S. It functions by interrupting the current in the local loop between the telephone exchange and the calling party's telephone at a precise rate with a switch in the telephone that is operated by the rotary dial as it spins back to its rest position after having been rotated to each desired number.
In 1963, the Bell System introduced to the public its dual-tone multi-frequency (DTMF) technology under the name Touch-Tone, which was a trademark in the U.S. until 1984.

Vertical service code

calling featureservice featureCLASS
This led to the addition of the number sign octothorpe asterisk or "star" keys as well as a group of keys for menu selection: A, B, C and D. In the end, the lettered keys were dropped from most phones, and it was many years before the two symbol keys became widely used for vertical service codes such as *67 in the United States of America and Canada to suppress caller ID.
On a touch tone telephone, the codes are usually initiated with the star key, resulting in the commonly used name star codes.

Number sign

#hashhash symbol
This led to the addition of the number sign octothorpe asterisk or "star" keys as well as a group of keys for menu selection: A, B, C and D. In the end, the lettered keys were dropped from most phones, and it was many years before the two symbol keys became widely used for vertical service codes such as *67 in the United States of America and Canada to suppress caller ID.
Most scholars believe the word was invented by workers at the Bell Telephone Laboratories by 1968, who needed a word for the symbol on the telephone keypad. Don MacPherson is said to have created the word by combining octo and the last name of Jim Thorpe, an Olympic medalist. Howard Eby and Lauren Asplund claim to have invented the word as a joke in 1964, combining octo with the syllable therp which, because of the "th" digraph, was hard to pronounce in different languages. The Merriam-Webster New Book of Word Histories, 1991, has a long article that is consistent with Doug Kerr's essay, which says "octotherp" was the original spelling, and that the word arose in the 1960s among telephone engineers as a joke. Other hypotheses for the origin of the word include the last name of James Oglethorpe, or using the Old English word for village, thorp, because the symbol looks like a village surrounded by eight fields. The word was popularized within and outside Bell Labs. The first appearance of "octothorp" in a US patent is in a 1973 filing. This patent also refers to the six-pointed asterisk used on telephone buttons as a "sextile".

Goertzel algorithm

DTMF decoding algorithms typically use the Goertzel algorithm.
The Goertzel algorithm is a technique in digital signal processing (DSP) that provides a means for efficient evaluation of individual terms of the discrete Fourier transform (DFT), thus making it useful in certain practical applications, such as recognition of DTMF tones produced by the buttons pushed on a telephone keypad.

Selective calling

two-tone sequential pagingMotorola Quik Call Ipulsed radio codes
Selective calling
Selective calling systems can overlap; a radio may have (group call) and DTMF individual calling.

Voice over IP

VoIPvoice over Internet Protocolvoice-over-IP
In IP telephony, DTMF signals can also be delivered as either in-band or out-of-band tones, or even as a part of signaling protocols, as long as both endpoints agree on a common approach to adopt.
Most analog telephone adapters do not decode dial pulses generated by rotary dial telephones, but rather support only touch-tone signaling, but pulse-to-tone converters are commercially available.

Caller ID

caller line identificationCLIcall display
This led to the addition of the number sign octothorpe asterisk or "star" keys as well as a group of keys for menu selection: A, B, C and D. In the end, the lettered keys were dropped from most phones, and it was many years before the two symbol keys became widely used for vertical service codes such as *67 in the United States of America and Canada to suppress caller ID. DTMF tones are used in some caller ID systems to transfer the caller ID information, but in the United States only Bell 202 modulated FSK signaling is used to transfer the data.
Instead of Bell 202, the European alternative V.23 is sometimes used, (without the 75-baud reverse channel) or the data is sent using DTMF signalling.

Asterisk

*asterisksstar
This led to the addition of the number sign octothorpe asterisk or "star" keys as well as a group of keys for menu selection: A, B, C and D. In the end, the lettered keys were dropped from most phones, and it was many years before the two symbol keys became widely used for vertical service codes such as *67 in the United States of America and Canada to suppress caller ID.
On a Touch-Tone telephone keypad, the asterisk (called star, or less commonly, palm or sextile) is one of the two special keys (the other is the number sign (pound sign or hash, hex or, less commonly, octothorp or square)), and is found to the left of the zero.

Autovon

Automatic Voice Networkmultilevelmultilevel precedence and preemption
The AUTOVON telephone system of the United States Armed Forces used these signals to assert certain privilege and priority levels when placing telephone calls.
These levels were activated using the buttons in an additional column of the keypad, which produced the dual-tone multi-frequency (DTMF) signals A, B, C, and D:

Frequency-shift keying

FSKfrequency shift keyingaudio frequency-shift keying
DTMF tones are used in some caller ID systems to transfer the caller ID information, but in the United States only Bell 202 modulated FSK signaling is used to transfer the data.
In some countries of Europe, the European Telecommunications Standards Institute (ETSI) standards 200 778-1 and -2 – replacing 300 778-1 & -2 – allow 3 physical transport layers (Telcordia Technologies (formerly Bellcore), British Telecom (BT) and Cable Communications Association (CCA)), combined with 2 data formats Multiple Data Message Format (MDMF) & Single Data Message Format (SDMF), plus the Dual-tone multi-frequency (DTMF) system and a no-ring mode for meter-reading and the like.

Bell System

BellBell Operating CompaniesBell Telephone
DTMF was first developed in the Bell System in the United States, and became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963.

Landline

fixed linefixed-lineland line
The Touch-Tone system using a telephone keypad gradually replaced the use of rotary dial and has become the industry standard for landline and mobile service.

Local loop

subscriber lineloopsubscriber loop
Prior to the development of DTMF, telephone numbers were dialed by users with a loop-disconnect (LD) signaling, more commonly known as pulse dialing (dial pulse, DP) in the U.S. It functions by interrupting the current in the local loop between the telephone exchange and the calling party's telephone at a precise rate with a switch in the telephone that is operated by the rotary dial as it spins back to its rest position after having been rotated to each desired number.

Calling party

callercall originatorcall
Prior to the development of DTMF, telephone numbers were dialed by users with a loop-disconnect (LD) signaling, more commonly known as pulse dialing (dial pulse, DP) in the U.S. It functions by interrupting the current in the local loop between the telephone exchange and the calling party's telephone at a precise rate with a switch in the telephone that is operated by the rotary dial as it spins back to its rest position after having been rotated to each desired number.

Subscriber trunk dialling

STDSTD code487
Placing calls over longer distances required either operator assistance or provision of special subscriber trunk dialing equipment.

Pure tone

tonepure sinusoidal tonesine tones
Multi-frequency signaling (MF) is a group of signaling methods that use a mixture of two pure tone (pure sine wave) sounds.

Sine wave

sinusoidalsinusoidsine
Multi-frequency signaling (MF) is a group of signaling methods that use a mixture of two pure tone (pure sine wave) sounds.