DTMF stands for "Dual-Tone Multi-Frequency." It is a telecommunication signalling feature used in a VoIP (Voice over Internet Protocol) system. "In-band" signalling is the process of sending metadata and control information within the same band and on the same channel. When you dial a number, it is encoded and transmitted across a telephone line as Dual-Tone Multi-Frequency (DTMF) tones. As an administrator, you can test your DTMF on an Asterisk server using the "Dial" command.
Log in to an Asterisk server using administrative credentials.
Double-click to open a "Command prompt" or "Terminal window" (depending on your system) from the desktop.
Type the following without the quotes:
Press the "Enter" key. Replace "<num>" with your own VoIP number, and replace "<peer>" with the VoIP number of your contact. The "W" causes the pause when you enter this command. For example: "Dial(5551112222@3334447777,180,D(w*w1w3))."