September 2008
Intermediate to advanced
550 pages
18h 10m
English
Content preview from VoIP Voice and Fax Signal ProcessingBecome an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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7
DTMF DETECTION, GENERATION, AND REJECTION
DTMF is a dual-tone multifrequency signaling tone generated while pressing the telephone keypad numbers in tone mode. It is known by several names, including multiple frequency push button (MFPB) and digit tones, but the most well known is DTMF. When a key is pressed on a telephone keypad, the telephone typically generates a dual-frequency tone composed of a low-frequency component and a high-frequency component, which is recognized by equipment connected to the phone. This method of signaling replaces an older method known as pulse dialing where the number entered is represented by a series of line make-and-break contacts that result in electrical pulses. In pulse dialing, a single pulse represents one, and two pulses represent two, and ten pulses represent zero. Often modern phones support both methods, typically by setting a pulse/tone switch on the phone. Currently, DTMF is the most popular dialing in use.
DTMF-based signaling is used in many telecommunication applications, including public switched telephone network (PSTN) telephony, VoIP, answering machines, Internet Protocol Private branch exchange (IP PBX), telephone exchanges, video conferencing, video phones, IP phones, voice messaging systems, wireless telephony, and interactive voice message announcement systems. The telephone keypad has keys with the digits 0 through 9 and the symbols hash (#), star (*), and other feature [ITU-T-Q.23 (1988), TIA/EIA-464C (2001)] keys known ...
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