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Monday, November 21, 2011

Dual-tone multi-frequency signaling (DTMF)

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.

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.

2 comments:

  1. Nice sharing thanks for the post. You have provided nice post I’ll bookmark your blog and read this kind of stuff very often. Keep updating it I will be following it.

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  2. I use Speedy and also cbn. But I don't understand why I need to have both, as advised by cbn -after all, Speedy is meant to connect us to Internet, etc. If I use, say, Gmail instead of cbn are there any problems that might leap up and hit me later on?

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