Dtmf; Methods Of Transmitting Dtmf Digits On Sip Calls - Matrix SPARSH VP710 User Manual

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DTMF

DTMF (Dual Tone Multi-frequency) also known as touch-tone is used for telecommunication 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 when the keypad of the IP phone is pressed during a call.

Each key pressed on the IP phone generates one sinusoidal tone of two frequencies. One is generated from a high

frequency group and the other from a low frequency group.

The DTMF keypad is laid out in a 4 × 4 matrix, with each row representing a low frequency, and each column

representing a high frequency. Pressing a digit key (such as '1') will generate a sinusoidal tone for each of the two

frequencies (697 and 1209 hertz (Hz)).

DTMF Keypad Frequencies:

The method of transmitting DTMF digits is configurable on a per-line basis.

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 SIP INFO messages.

DTMF digits are transmitted using the RTP Event packets that are sent along with the voice path. These packets

use RFC 2833 format and must have a payload type that matches what the other end is listening for. The payload

type for RTP Event packets is configurable. IP phones default to 101 for the payload type, which use the definition

to negotiate with the other end during call establishment.

The RTP Event packet contains 4 bytes. The 4 bytes are distributed 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.

DTMF digits are transmitted within the audio of the IP phone conversation. It uses the same codec as your voice

and is audible to conversation partners.

Matrix SPARSH VP710 User Guide