Telecommunications

011 44

+ 44 from anywhere. In the US replace + with 011.

Dual-tone multi-frequency signaling (DTMF) is used for telecommunication signaling over analog telephone lines in the voice-frequency band between telephone handsets and other communications devices and the switching center. The version of DTMF that is used in push-button telephones for tone dialing is known as Touch-Tone. It was developed by Western Electric and first used by the Bell System in commerce, using that name as a registered trademark. DTMF is standardized by ITU-T Recommendation Q.23. It is also known in the UK as MF4.

Other multi-frequency systems are used for internal signaling within the telephone network.

Introduced by AT&T in 1963,[1] the Touch-Tone system using the telephone keypad gradually replaced the use of rotary dial and has become the industry standard for landline service.

Prior to the development of DTMF, numbers were dialed on automated telephone systems by means of pulse dialing (Dial Pulse or DP in the U.S.) or loop disconnect (LD) signaling, which functions by rapidly disconnecting and re-connecting the calling party's telephone line, similar to flicking a light switch on and off. The repeated interruptions of the line, as the dial spins, sounds like a series of clicks. The exchange equipment interprets these dial pulses to determine the dialed number. Loop disconnect range was restricted by telegraphic distortion and other technical problems[which?], and placing calls over longer distances required either operator assistance (operators used an earlier kind of multi-frequency dial) or the provision of subscriber trunk dialing equipment.

Multi-frequency signaling (see also MF) 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 (DTMF) signaling was developed for the consumer to signal their own telephone-call's destination telephone number instead of talking to a telephone operator.

AT&Ts Compatibility Bulletin No. 105 described the product as "a method for pushbutton signaling from customer stations using the voice transmission path." In order to prevent consumer telephones from interfering with the MF-based routing and switching between telephone switching centers, DTMF's 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, as used in push-button telephone tone dialing, was known throughout the Bell System by the trademark Touch-Tone. This term was first used by AT&T in commerce on July 5, 1960 and then was introduced to the public on November 18, 1963, when the first push-button telephone was made available to the public. It was AT&T's registered trademark from September 4, 1962 to March 13, 1984,[2] and is standardized by ITU-T Recommendation Q.23. It is also known in the UK as MF4.

Other vendors of compatible telephone equipment called the Touch-Tone feature Tone dialing or DTMF, or used their own registered trade names such as the Digitone of Northern Electric (now known as Nortel Networks).

The DTMF system uses eight different frequency signals transmitted in pairs to represent 16 different numbers, symbols and letters - as detailed below.

As a method of in-band signaling, DTMF tones 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 better out-of-band signaling equipment was developed in the 1990s, fast, unacknowledged, and loud DTMF tone sequences could be heard during the commercial breaks of cable channels in the United States and elsewhere.

He was known for his theory of electromagnetism where much of modern technology in the telecommunication industry owe their existence.

He present a theory that explains the relationship between electric and magnetic phenomenon.

AM has a frequency range of 531 kHz to 1602 kHz and on the other hand FM has a frequency range between 8705 MHz to 108 MHz. If we talk about the bandwidth of AM then it is 1071 KHz and bandwidth of FM is 20.5 MHz.

According to the bandwidth FM should be used for long distance transmission but it is not used for long distance but AM is used fir long distance transmissions. the answer is here.

Long distance transmissions are also decided by the Spectrum of the Signal in frequency domain by doing the Fouriertransform of the Signal.

If we draw the Spectrum of AM waves the we find that their is a main loop in the central part of the spectrum with a high frequency and on the left and right side of this loop their are side loop which are very smaller then the main loop. In FM information can be recover from the main loop only not from the side loops. On the other hand in AM waves all the loops in spectrum is of same size and information can be recover from all the loops.

That is why AM is used for long distance transmission.

Thnx -Vipin Jasoria