Chapter 7

DTMF Interworking

At some point, you have heard a prerecorded prompt requesting some information, perhaps a credit card number or an employee number. After a couple of presses on the keypad, you magically get the information you were looking for or are connected to a human agent. The underlying framework that enables this seamless transfer of information is known as dual-tone multifrequency (DTMF).

With the advent of voice over IP (VoIP), reliable transmission of keypad button presses end to end became somewhat of a problem, as audio codecs were not optimized for carrying DTMF tones without bringing in a degree of distortion. There was need to engineer a new way of reliably transmitting DTMF. This solution aimed to factor in all the ...

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