Dual-tone multi-frequency signaling - Wikipedia
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`Dual-tone multi-frequency signaling
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`"Tone dialing" redirects here. For Ornette Coleman album, see Tone Dialing (album).
`For the video game, see TouchTone.
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`Dual-tone multi-frequency signaling (DTMF) is an in-
`band telecommunication signaling system using the
`voice-frequency band over telephone lines between
`telephone equipment and other communications
`devices and switching centers. 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.[1] DTMF is standardized by
`ITU-T Recommendation Q.23 . It is also known in the
`UK as MF4.
`
`The keypads on telephones for the
`Autovon systems used all 16 DTMF
`signals. The red keys in the fourth
`column produce the A, B, C, and D
`DTMF events.
`
`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. Other multi-frequency systems
`are used for internal signaling within the telephone network.
`
`Contents [hide]
`1 Multifrequency signaling
`2 #, *, A, B, C, and D
`3 Keypad
`4 Decoding
`5 Other multiple frequency signals
`6 See also
`7 References
`8 Further reading
`9 External links
`
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`Dual-tone multi-frequency signaling - Wikipedia
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`Multifrequency signaling [edit]
`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.
`The exchange equipment responds to the dial pulses either directly by operating relays, or by
`storing the number in a digit register recording the dialed number. The physical distance for
`which this type of dialing was possible was restricted by electrical distortions and was only
`possible on direct metallic links between end points of a line. Placing calls over longer distances
`required either operator assistance or provision of special subscriber trunk dialing equipment.
`Operators used an earlier type of multi-frequency signaling.
`
`Multi-frequency signaling is a group of signaling methods that use a mixture of two pure tone
`(pure sine wave) sounds. Various MF signaling protocols were devised by the Bell System and
`CCITT. 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.
`This semi-automated signaling and switching proved successful in both speed and cost
`effectiveness. Based on this prior success with using MF by specialists to establish long-
`distance telephone calls, dual-tone multi-frequency signaling was developed for end-user
`signaling without the assistance of operators.
`
`The DTMF system uses a set of eight audio frequencies transmitted in pairs to represent 16
`signals, represented by the ten digits, the letters A to D, and the symbols # and *. As the signals
`are audible tones in the voice frequency range, they can be transmitted through electrical
`repeaters and amplifiers, and over radio and microwave links, thus eliminating the need for
`intermediate operators on long-distance circuits.
`
`AT&T described the product as "a method for pushbutton signaling from customer stations using
`the voice transmission path."[2] In order to prevent consumer telephones from interfering with the
`MF-based routing and switching between telephone switching centers, DTMF frequencies differ
`from all of the pre-existing MF signaling protocols between switching centers: MF/R1, R2, CCS4,
`CCS5, and others that were later replaced by SS7 digital signaling. DTMF was known
`throughout the Bell System by the trademark Touch-Tone. The term was first used by AT&T in
`commerce on July 5, 1960 and was introduced to the public on November 18, 1963, when the
`first push-button telephone was made available to the public. It was a registered trademark by
`AT&T from September 4, 1962 to March 13, 1984. It is standardized by ITU-T Recommendation
`Q.23. In the UK, it is also known as MF4.
`
`Other vendors of compatible telephone equipment called the Touch-Tone feature tone dialing or
`DTMF, or used their other trade names such as Digitone by Northern Electric Company in
`Canada.
`
`As a method of in-band signaling, DTMF signals were also used by cable television
`broadcasters to indicate the start and stop times of local commercial insertion points during
`station breaks for the benefit of cable companies. Until out-of-band signaling equipment was
`
`https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling[12/8/2016 11:28:23 AM]
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`

`
`Dual-tone multi-frequency signaling - Wikipedia
`
`developed in the 1990s, fast, unacknowledged DTMF tone sequences could be heard during the
`commercial breaks of cable channels in the United States and elsewhere.[citation needed]
`Previously, terrestrial television stations used DTMF tones to control remote
`transmitters.[citation needed]
`
`#, *, A, B, C, and D [edit]
`The engineers had envisioned telephones being used to
`access computers, and automated response systems.
`They consulted with companies to determine the
`requirements. This led to the addition of the number
`sign (#, ''pound'' or "diamond" in this context, "hash",
`"square" or "gate" in the UK, and "octothorpe'' by the
`original engineers) and 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.
`
`Public payphones that accept credit cards
`use these additional codes to send the
`information from the magnetic strip.
`
`DTMF keypad layout.
`
`DTMF dialing
`
`0:00
`How DTMF dialing sounds.
`
`MENU
`
`The AUTOVON telephone system of the
`United States Armed Forces used these signals to assert certain privilege and priority levels
`when placing telephone calls.[3] Precedence is still a feature of military telephone networks, but
`using number combinations. For example, entering 93 before a number is a priority call.
`
`Problems playing this file? See media help.
`
`Present-day uses of the A, B, C and D signals on telephone networks are few, and are exclusive
`to network control. For example, the A key is used on some networks to cycle through different
`carriers at will. The A, B, C and D tones are used in radio phone patch and repeater operations
`to allow, among other uses, control of the repeater while connected to an active phone line.
`
`The *, #, A, B, C and D keys are still widely used worldwide by amateur radio operators and
`commercial two-way radio systems for equipment control, repeater control, remote-base
`operations and some telephone communications systems.
`
`DTMF signaling tones can also be heard at the start or end of some VHS (Video Home System)
`cassette tapes. Information on the master version of the video tape is encoded in the DTMF
`tone. The encoded tone provides information to automatic duplication machines, such as format,
`duration and volume levels, in order to replicate the original video as closely as possible.
`
`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.
`
`Keypad [edit]
`
`https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling[12/8/2016 11:28:23 AM]
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`Papst Licensing GmbH & Co. KG's Preliminary Response - Ex. 2004, p. 3
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`
`Dual-tone multi-frequency signaling - Wikipedia
`
`1209 Hz on 697 Hz to make the 1
`tone
`
`The DTMF telephone keypad is laid out in a 4×4 matrix
`of push buttons in which each row represents the low
`frequency component and each column represents the
`high frequency component of the DTMF signal.
`Pressing a key sends a combination of the row and
`column frequencies. For example, the key 1 produces a
`superimposition of tones of 697 and 1209 hertz (Hz).
`Initial pushbutton designs employed levers, so that each
`button activated two contacts. The tones are decoded
`by the switching center to determine the keys pressed
`by the user.
`
`DTMF keypad frequencies (with sound clips)
`1209 Hz 1336 Hz 1477 Hz 1633 Hz
`1
`2
`3
`A
`4
`5
`6
`B
`7
`8
`9
`C
`*
`0
`#
`D
`
`697 Hz
`770 Hz
`852 Hz
`941 Hz
`
`Decoding [edit]
`DTMF was originally decoded by tuned filter banks. By
`the end of the 20th century, digital signal processing
`became the predominant technology for decoding.
`DTMF decoding algorithms often use the Goertzel
`algorithm to detect tones.
`
`Other multiple frequency signals [edit]
`National telephone systems define other tones that indicate the status of lines, equipment, or the
`result of calls. Such call-progress tones are often also composed of multiple frequencies and are
`standardized in each country. The Bell System defines them in the Precise Tone Plan.[4]
`However, such signaling systems are not considered to belong to the DTMF system.
`
`2 DTMF Receiver CMD CM8870CSI
`
`See also [edit]
`Selective calling
`Special information tones
`
`References [edit]
`1. ^ Dodd, Annabel Z. The essential guide to telecommunications. Prentice Hall PTR, 2002, p. 183.
`2. ^ AT&T, Compatibility Bulletin No. 105
`3. ^ "What are the ABCD tones?" — Tech FAQ
`4. ^ AT&T (1968), "Notes on Distance Dialing"
`
`https://en.wikipedia.org/wiki/Dual-tone_multi-frequency_signaling[12/8/2016 11:28:23 AM]
`
`Papst Licensing GmbH & Co. KG's Preliminary Response - Ex. 2004, p. 4
`
`

`
`Dual-tone multi-frequency signaling - Wikipedia
`
`Further reading [edit]
`ITU's recommendations for implementing DTMF services
`Schenker, L (1960), "Pushbutton Calling with a Two-Group Voice-Frequency Code"
`The Bell System Technical Journal, 39 (1): 235–255, ISSN 0005-8580 .
`Deininger, R.L. (July 4, 1960). "Human Factors Engineering Studies of the Design and Use
`. Bell System Technical Journal. 39 (4): 995–1012.
`of Pushbutton Telephone Sets"
`Frank Durda, Dual Tone Multi-Frequency (Touch-Tone®) Reference , 2006.
`ITU-T Recommendation Q.24 - Multifrequency push-button signal reception
`
` (PDF),
`
`External links [edit]
`ITU-T Recommendation Q.23 - Technical features of push-button telephone sets
`
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`This page was last modified on 24 November 2016, at 01:55.
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