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.
When
we consider dialing numbers in the telephone now days commonly uses DTMF. Using
DTMF (dual tone multi frequency) when we press a key on our phone, it generates
two tones of specific frequencies. Then the signal is encoded as a pair of
sinusoidal (sine wave) tones from the table below which are mixed with each
other. The mixed frequency is traveled to the exchange.
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| DTMF |
Advantages of DTMF compare to Rotary
Dialing
The
main advantage is easy to access the phone when we are taking a call. But using
rotary dialing hard to make a call.
When
we are taking a call, in rotary dialing we have to rotate the numbers. Rotary
dial pulses cannot pass through a central exchange. It is time consuming.
Normally it takes an average of about 1.5 seconds per digit, or 15 seconds for
dialing a 10-digit number. But DTMF tones can pass through a central exchange.
It is recognized by the register at the central exchange. A DTMF tone must be
present for a minimum of 40 ms. Between two consecutive digits, a pause of 60
ms is required. Total time needed for transmission of one digit is about 100
ms. Compare to rotary dialing it takes very much low of time .It is more efficient
than rotary dialing.
