Dual-tone multi-frequency signaling

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Multi-tone multi-tone marking ( DTMF ) is a telecommunication signaling system in the band using a voice frequency band through a telephone line between telephone equipment and other communications devices and central switching. DTMF was first developed at the Bell System in the United States, and became known under the Touch-Tone trademark for use in push-button phones supplied to telephone subscribers, beginning in 1963. DTMF standardized as ITU -T Recommendation Q.23. It is also known in the UK as MF4 .

The Touch Tone system using the phone keys gradually replaces the use of rotary rotation and has become the industry standard for landlines and cellular services. Other multi-frequency systems are used for internal signaling in the telephone network.

Video Dual-tone multi-frequency signaling

Multi-functional multifunctional signal

Prior to DTMF development, phone numbers were contacted by users with loop-disconnect (LD) signaling, better known as dial pulse (DP) in the US. This works by interrupting the current in the local loop between the telephone exchange and the calling party telephone at the right level with a switch on the phone operated by a rotary loop as it rotates back to its resting position after it is rotated to each desired number. The exchange equipment responds to the call pulse either directly by operating the relay, or by storing the number in the register digit recording the dialed number. The physical distance that allows this type of call is limited by electrical distortion and is only possible on direct metal relations between the end points of a line. Placing calls over a longer distance requires operator assistance or the provision of specialized customer channel dialing equipment. The operator uses the previous multi-frequency signaling type.

Multi-frequency signaling (MF) is a group of signaling methods that use a mixture of two pure sounds (pure sine wave). Various MF signaling protocols are designed by the Bell System and CCITT. The earliest of these are for in-band signaling between switching centers, where long distance phone operators use a 16-digit keypad to enter the next part of the destination phone number to contact the next downstream telephony operator next. These semi-automated signals and redirects proved successful both in speed and cost effectiveness. Based on previous successes using MF by specialists for making long distance phone calls, dual-tone multi-frequency signaling is developed for end-user signaling without operator assistance.

The DTMF system uses a set of eight audio frequencies sent in pairs to represent 16 signals, represented by ten digits, letters A to D, and symbols # and * . Since the signal is a audible tone within the sound frequency range, signals can be transmitted through electrical repeater and amplifiers, and over radio and microwave connections, eliminating the need for intermediate operators on remote circuits.

AT & T describes the product as "a method for signaling pushbuttons from customer stations using voice transmission lines." To prevent consumer calls from disrupting MF-based routes and switching between telephone switching centers, DTMF frequencies differ from all existing MF signaling protocols between switching centers: MF/R1, R2, CCS4, CCS5, and others. which was later replaced by SS7 digital signaling. DTMF is known throughout the Bell System by the trademark of Touch-Tone . The term was first used by AT & T in trading on July 5, 1960 and was introduced to the public on November 18, 1963, when the first push-button phone was made available to the public. It is a registered trademark by AT & amp; T from 4 September 1962 to 13 March 1984. This was standardized by the ITU-T Recommendation Q.23. In the UK, this is also known as MF4.

Other vendors of compatible phone equipment are called Tone-Touch tone dialing or DTMF features, or use other trade names such as Digitone by Northern Electric Company in Canada.

As an in-band signaling method, DTMF signals are also used by cable television broadcasters to indicate the start time and stop points of local commercial insertion during termination of the station for the benefit of the cable company. Until the out-of-band signing equipment was developed in the 1990s, the rapid and inaudible sequence of DTMF tones can be heard during the commercial breaks of cable channels in the United States and elsewhere. Previously, terrestrial television stations used DTMF tones to control remote transmitters.

Maps Dual-tone multi-frequency signaling

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

Engineers have imagined the phone being used to access computers and automated response systems. They consult with the company to determine the requirements. This led to the addition of the numbered sign (#, 'pound' or 'diamond' in this context, the English "hash", "square" or "gate" and "octothorpe" by the original engineers) and the asterisk or button "star" (*) as well as a bunch of buttons for menu selection: A, B, C and D. In the end, the letter keys are dropped from most phones, and many years before the symbol keys become widely used for the vertical service code such as * 67 in the United States and Canada to suppress caller ID.

Public telephones that accept credit cards use this extra code to send information from magnetic strips.

The US Armed Forces AUTOVON telephone system uses these signals to assert certain privileges and priority levels when making phone calls. Presence is still a feature of the military telephone network, but uses a combination of numbers. For example, entering 93 before a number is a priority call.

Current usage of the A, B, C and D signals on the telephone network is small, and exclusive to network control. For example, A key is used on some networks to rotate different operators as desired. Tones A, B, C, and D are used in the patch and operation of radio telephone repeaters to allow, among other uses, repeater controls when connected to an active telephone line.

Keys *, #, 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 operation and some telephone communication systems.

DTMF signal tones can also be heard at the beginning or end of some VHS cassette tapes (Video Home System). Information about the master version of the video tape is encoded in DTMF tones. Encoded tones provide information to automatic duplicating machines, such as format, duration and volume levels, to replicate original videos to the fullest.

DTMF tones are used in some caller ID systems to transfer caller ID information, but in the United States only Bell Function termination Bell 202 is used to transfer data.

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Keypad

DTMF phone keys are placed as button matrices where each row represents a low frequency component and each column represents a high frequency component of the DTMF signal. There are four rows and usually three columns, although the fourth column may exist for some apps. Pressing the button sends a combination of line and column frequencies. For example, the 1 button produces a low tone superimposition of 697 Hz and a high tone of 1209 Hz. The original button design used the lever, allowing each button to activate one row and one contact column. The tones are translated by the switching center to determine which buttons are pressed by the user.

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Decoding

DTMF was originally translated by filter bank set. At the end of the 20th century, digital signal processing became the main technology for decoding. DTMF decoding algorithm usually uses Goertzel algorithm. Because DTMF signaling is often transmitted in-band with sound or other audio signals present simultaneously, the DTMF signal definition includes strict limits for timing (minimum duration and interdigit distance), frequency deviations, harmonics, and amplitude relationships of two components with respect to one the other ( twist ).

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Other multi-frequency signals

The national telephone system determines other tones that indicate the status of channels, equipment, or call results. Such call-forward tones often also consist of several frequencies and are standardized in each country. The Bell System defines them in the Right Tune Plan. However, such signaling systems are not considered to belong to the DTMF system.

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References

dtmf circuit Page 2 : Telephone Circuits :: Next.gr

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Dual-tone multi-frequency signaling

Rabu, 20 Juni 2018