Specifications

Chapter 10 - Voice Transmissions DTMF Detection
140
Mediatrix 4100
2. Restart the Mediatrix 4100 so that the changes may take effect.
DTMF Payload Type
When selecting the outOfBandUsingRtp DTMF transport mode (see “DTMF Transport Type” on page 139 for
more details), you can determine the actual RTP dynamic payload type used for the “telephone-event” in an
initial offer. The payload types available are as per RFC 1890.
 To define the DTMF payload type:
1. In the voiceIfMIB, set the DTMF transport type in the voiceIfDtmfTransport variable
(voiceIfDtmfTransportTable group) to outOfBandUsingRtp.
2. Set the payload type in the voiceIfDtmfPayloadType variable.
Available values range from 96 to 127.
DTMF Detection
The default DTMF detection parameters of the Mediatrix 4100 may sometimes not be enough to properly
detect the DTMFs. This section describes how to set additional DTMF detection parameters.
DTMF Frequencies
The DTMF keypad is laid out in a 4x4 matrix, with each row representing a low frequency, and each column
representing a high frequency. For example, pressing a single key (such as '1') sends a sinusoidal tone of the
two frequencies (697 Hz and 1209 Hz). When the unit is configured to send DTMFs out-of-band, its DSP
detects these DTMFs, removes them from the RTP stream, and sends them out-of-band.
DTMF Detection Configuration
Below is a frequency spectrum analysis of a DTMF (9) with the Frequency in Hertz on the x axis and the Power
in dBm on the y axis. The low and high frequencies of the DTMF are in red and you can clearly see that they
are the most powerful frequencies in the signal.
outOfBandUsingSignalingProtocol The DTMFs are transmitted as per the MGCP protocol
standard.
signalingProtocolDependent The signalling protocol has the control to select the DTMF
transport mode.
Table 101: DTMF Transport Type Parameters (Continued)
Transport Parameter Description
Standards Supported • RFC 1890 – RTP Profile for Audio and Video Conferences
with Minimal Control
Table 102: DTMF Keypad Frequencies
Low/High (Hz) 1209 1336 1477 1633
697 123A
770 456B
852 789C
941 *0#D