DTMF

Source: Wikipedia, the free encyclopedia.
"Tone dialing" redirects here. For the Ornette Coleman album, see
Tone Dialing (album)
.
For the video game, see TouchTone.
Autovon keypads were one of the few production units to include all 16 DTMF signals. The red keys in the fourth column produce the A, B, C, and D DTMF events.

Dual-tone multi-frequency signaling (DTMF) is a

switching centers.[1] 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. DTMF is standardized as ITU-T Recommendation Q.23.[2]
It is also known in the UK as MF4.

Touch-Tone dialing with a

multi-frequency
systems are also used for signaling on trunks in the telephone network.

Multifrequency signaling

Before the development of DTMF, telephone numbers were dialed by users with a loop-disconnect (LD) signaling, more commonly known as

multi-frequency
signaling.

Multi-frequency signaling (MF) is a group of signaling methods that use a mixture of two

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".

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. As a parent company of Bell Systems, AT&T held the trademark from September 4, 1962, to March 13, 1984.[4] 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. Automatic Electric (GTE) referred to it as "Touch-calling" in their marketing. Other trade names such as Digitone were used by the

Northern Electric Company
in Canada.

As a method of

IP telephony, DTMF signals can also be delivered as either in-band or out-of-band tones,[7] or even as a part of signaling protocols,[8]
as long as both endpoints agree on a common approach to adopt.

Keypad

DTMF keypad layout.
Combination of 1209 Hz and 697 Hz sine waves, representing DTMF "1"

The DTMF telephone keypad is laid out as a 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. The commonly used keypad has four rows and three columns, but a fourth column is present for some applications. Pressing a key sends a combination of the row and column frequencies. For example, the 1 key produces a superimposition of a 697 Hz low tone and a 1209 Hz high tone. Initial pushbutton designs employed levers, enabling each button to activate one row and one column contact. The tones are decoded by the switching center to determine the keys pressed by the user.

DTMF keypad frequencies (with sound clips)[9]
1209 Hz 1336 Hz 1477 Hz 1633 Hz
697 Hz 1ⓘ 2ⓘ 3ⓘ Aⓘ
770 Hz 4ⓘ 5ⓘ 6ⓘ Bⓘ
852 Hz 7ⓘ 8ⓘ 9ⓘ Cⓘ
941 Hz *ⓘ 0ⓘ #ⓘ Dⓘ

#, *, A, B, C, and D

DTMF dialing
audio output of a DTMF signal.
Problems playing this file? See media help.

Engineers had envisioned telephones being used to access computers and automated response systems.[10] 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 keypads and it was many years before the two symbol keys became widely used for vertical service codes such as *67 in the United States and Canada to suppress caller ID.

Public

magnetic strip
.

The

AUTOVON telephone system of the United States Armed Forces used signals A, B, C, and D to assert certain privilege and priority levels when placing telephone calls.[11]
Precedence is still a feature of military telephone networks, but using number combinations. For example, entering 93 before a number is a priority call.

Present-day uses of the signals A, B, C and D are rare in telephone networks, and are exclusive to network control. For example, A is used in some networks for cycling through a list of carriers.[citation needed] The signals are used in radio phone patch and repeater operations to allow, among other uses, control of the repeater while connected to an active telephone line.[citation needed]

The signals *, #, A, B, C and D 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.[citation needed]

DTMF signaling tones may also be heard at the start or end of some prerecorded VHS videocassettes.[12] Information on the master version of the video tape is encoded in the DTMF tones. The encoded tones provide 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, a function that is performed in the United States by Bell 202 modulated frequency-shift keying (FSK) signaling.

Decoding

Two CMD CM8870CSI DTMF Receivers

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 typically use the Goertzel algorithm although application of MUSIC (algorithm) to DTMF decoding has been shown to outperform Goertzel and being the only possibility in cases when number of available samples is limited.[13] As DTMF signaling is often transmitted in-band with voice or other audio signals present simultaneously, the DTMF signal definition includes strict limits for timing (minimum duration and interdigit spacing), frequency deviations, harmonics, and amplitude relation of the two components with respect to each other (twist).[14]

Other multiple frequency signals

National telephone systems define other tones, outside the DTMF specification, that indicate the status of lines, equipment, or the result of calls, and for control of equipment for troubleshooting or service purposes. Such

Precise Tone Plan.[15] Bell's Multi-frequency signaling was exploited by blue box
devices.

Some early modems were based on touch-tone frequencies, such as Bell 400-style modems.[9]

See also

References

  1. OCLC 779863446.{{cite book}}: CS1 maint: multiple names: authors list (link
    )
  2. ^ Technical features of push-button telephone sets (Report). Recommendation. ITU. Q.23.
  3. ^ AT&T, Compatibility Bulletin No. 105
  4. ^ "TESS -- Error".
  5. ^ "DISH NETWORK L.L.C., INTERNATIONAL AFFILIATION AGREEMENT: Metro Media Holding Corp (Filer)". U.S. Securities and Exchange Commission. 27 January 2016. S.E.C. Accession No. 0001557234-16-000400. Retrieved 26 April 2020. Cue Tones: Within four (4) months after the Launch Date, Network shall deliver the Signal with industry standard DTMF cue tones for the insertion of up to a maximum of twelve (12) minutes per hour of commercial advertising time. Until such cue tones are delivered or at any time thereafter upon DISH's request, DISH may deliver all or part of its Advertising Allocation to Network via FTP or courier, at Network's sole cost and expense, and Network shall insert such Advertising Allocation at Network's sole cost and expense.
  6. ^ "In the Matter of Amendment of Part 73, Subpart G, of the Commission's Rules Regarding the Emergency Broadcast System, REPORT AND ORDER AND FURTHER NOTICE OF PROPOSED RULE MAKING, B. Cable participants § 63,65" (PDF). Washington, D.C.: Federal Communications Commission. 9 December 1994. p. 23. FCC 94-288. Retrieved 26 April 2020. Dual Tone Multi-Frequency: The Society of Cable Television Engineers (SCTE) reported that many cable systems have installed Dual Tone Multi-Frequency (DTMF) signalling equipment between the cable system and local officials for use in transmitting emergency information as part of the local franchise agreement. The SCTE recommended that DTMF decoding be incorporated in the new equipment since it is already used by many cable systems. The new EAS code protocol will be a national standard and should exceed the capabilities of DTMF. Local emergency managers will find the EAS equipment much more flexible than DTMF equipment. For example, they will be able to access EAS equipment at cable headends directly. The emergency messages in the EAS protocol will also be available to local broadcast stations and NWS offices for further dissemination.
  7. ^ H. Schulzrinne and T. Taylor, RTP Payload for DTMF Digits, Telephony Tones, and Telephony Signals, IETF RFC 4733, December 2006.
  8. ^ C. Holmberg, E. Burger, H. Kaplan, Session Initiation Protocol (SIP) INFO Method and Package Framework, IETF RFC 6086, January 2011.
  9. ^ a b Don Lancaster. "TV Typewriter Cookbook". (TV Typewriter). Section "400-Style (Touch-Tone) Modems". p. 177-178.
  10. ISBN 978-0-393-24154-9
    .
  11. ^ ""What are the ABCD tones?" — Tech FAQ". 6 April 2019.
  12. ^ Broadcast Engineering. Intertec Publishing Corporation], $4c 1959. 1983.
  13. ^ "P. Gregor, Application of MUSIC algorithm to DTMF detection, Engineering Thesis, Warsaw University of Technology, 2022". {{cite journal}}: Cite journal requires |journal= (help)
  14. ^ W. D. Reeves, Subscriber Loop Signaling and Transmission Handbook—Analog, IEEE (1992), p.27
  15. ^ AT&T, Notes on Distance Dialing, 1968

Further reading

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