Configuring Basic Features105DTMF (Dual Tone Multi-frequency), better known as touch-tone, is used fortelecommunication signaling over analog telephone lines in the voice-frequency band.DTMF is the signal sent from the IP phone to the network, which is generated whenpressing the IP phone’s keypad during a call. Each key press on the IP phone generatesone sinusoidal tone of two frequencies. One is generated from a high frequency groupand the other from a low frequency group.The DTMF keypad is laid out in a 4× 4 matrix, with each row representing a lowfrequency, and each column representing a high frequency. Pressing a digit key (suchas '1') will generate a sinusoidal tone for each of two frequencies (697 and 1209 hertz(Hz)).DTMF Keypad Frequencies:1209 Hz 1336 Hz 1447 Hz 1633 Hz697 Hz 1 2 3 A770 Hz 4 5 6 B852 Hz 7 8 9 C941 Hz * 0 # DThere are 3 common methods of transmitting DTMF digits on SIP calls: RFC 2833 – DTMF digits are transmitted by RTP Events compliant to RFC 2833. INBAND – DTMF digits are transmitted in the voice band. SIP INFO – DTMF digits are transmitted by the SIP INFO messages.The method of transmitting DTMF digits is configurable on a per-account basis.RFC 2833DTMF digits are transmitted using the RTP Event packets that are sent along with thevoice path. These packets use RFC 2833 format and must have a payload type thatmatches what the other end is listening for. The payload type for the RTP Event packetsis configurable. IP phones default to 101 for the payload type, which use the definition tonegotiate with the other end during call establishment.The RTP Event packet contains 4 bytes. The 4 bytes are distributed over several fieldsdenoted as Event, End bit, R-bit, Volume and Duration. If the End bit is set to 1, thepacket contains the end of the DTMF event. You can configure the number of times the IPphone sends the RTP Event packet with End bit set to 1.INBANDDTMF digits are transmitted within the audio of the IP phone conversation. It uses the
