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Voice Feature Guide 01

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Dual Tone Multi Frequency

Dual Tone Multi Frequency

Introduction

DTMF means that the tones of two frequencies are overlaid to represent a number, as shown in Table 1-6.

Table 1-6 Mapping between frequencies and numbers

Unit: Hz

1209

1336

1477

1633

697

1

2

3

A

770

4

5

6

B

852

7

8

9

C

941

*

0

#

D

When numbers are dialed on the phone, the dialed numbers are converted into the dual-frequency overlay tones. The DSP detects the dialed numbers by checking the DTMF.

The supported DTMF-specific functions are as follows:
  • DTMF erasure: After the DSP detects DTMF signals, it erases the DTMF signals from the RTP media stream.
  • DTMF transparent transmission: After the DSP detects DTMF signals, it retains the DTMF signals in the RTP media stream.
  • DTMF RFC2833 transmission: After the DSP detects DTMF signals, it erases the DTMF signals from the RTP media stream and sends the DTMF information in RFC2833 transmission mode.

Reference Standards and Protocols

ITU-T Q.24

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Updated: 2019-02-22

Document ID: EDOC1100067358

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