DTMF (Dual-tone multi-frequency signaling)

DTMF or dual-tone multi-frequency signaling is transmitting keystrokes during the call. It is most frequently used for transferring calls to PBX extension numbers, as well as call interception.

What DTMF features exist in Zadarma PBX?

In Zadarma PBX DTMF signaling is used for IVR (voice menu) during incoming calls.

DTMF features in PBX:

Call transferring

To transfer an incoming or outgoing call, press # followed by the extension number and another #, for example #101#

Call transfer with a voice note

To transfer a call with a voice note, press *, extension number and #, for example *101#

Call transfer to PBX scenario

To transfer a call to a scenario (a scenario can have several extension numbers, usually they are used for different departments), dial the voice menu scenario number, for example #1#

Call interception

To intercept an incoming call press 40 and the call button

I need to dial # or *

If you are calling from SIP (not PBX extension number), in DTMF # or * is transmitted in a regular way, as SIP does not have call transferring.

If you are initiating a call from PBX extension number to dial # or * during voice menu, enter 00# or 00*. Zeros will be deleted, and the system will only pass # or *.

DTMF signals can be transmitted in three ways:

• in-band: tones are transmitted in the voice stream without compression, this method only works when using в G.711 codec (PCM). It requires good quality internet connection.
• RFC2833: DTMF is transmitted separately from the voice stream, RTP EVENT protocol. This method works with any audio codec and does not depend on connection quality. DTMF packages will have Payload Type=101.
• SIP INFO: DTMF tones are transmitted in SIP-message INFO, dialed tones can be seen in SIP package in SDP.

When connecting to virtual PBX, method RFC2833 is required. If virtual PBX is inactive, any method can be used when transferring DTMF to Zadarma, on our side we only transfer tones in RFC2833 format.