Audio Features
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DTMF
DTMF (Dual Tone Multi-frequency) tone, better known as touch tone. DTMF is the signal sent from the IP phone to the
network, which is generated when pressing the IP phone’s keypad during a call. Each key pressed on the IP phone gen-
erates one sinusoidal tone of two frequencies. One is generated from a high-frequency group and the other from a
low-frequency group.
Topics
DTMF Keypad
Transmitting DTMF Digit
Suppress DTMF Display
Transfer via DTMF
Local DTMF Tone
DTMF Keypad
The DTMF keypad is laid out in a 4×4 matrix, with each row representing a low frequency, and each column rep-
resenting a high frequency. Pressing a digit key (such as '1') will generate a sinusoidal tone for each of two frequencies
(697 and 1209 hertz (Hz)).
DTMF Keypad Frequencies:
1209 Hz 1336 Hz 1477 Hz 1633 Hz
697 Hz 1 2 3 A
770 Hz 4 5 6 B
852 Hz 7 8 9 C
941 Hz * 0 # D
Note
The IP phones will not send DTMF sequence when the call is placed on hold or is held.
Transmitting DTMF Digit
Three methods of transmitting DTMF digits on SIP calls:
l RFC 2833 -- DTMF digits are transmitted by RTP Events compliant with RFC 2833. You can configure the payload
type and sending times of the end RTP Event packet. The RTP Event packet contains 4 bytes. The 4 bytes are dis-
tributed over several fields denoted as Event, End bit, R-bit, Volume and Duration. If the End bit is set to 1, the
packet contains the end of the DTMF event. You can configure the sending times of the end RTP Event packet.
l INBAND -- DTMF digits are transmitted in the voice band. It uses the same codec as your voice and is audible to
conversation partners.
l SIP INFO -- DTMF digits are transmitted by SIP INFO messages. DTMF digits are transmitted by the SIP INFO mes-
sages when the voice stream is established after a successful SIP 200 OK-ACK message sequence. The SIP INFO mes-
sage can transmit DTMF digits in three ways: DTMF, DTMF-Relay and Telephone-Event.
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