Dual-tone multi-frequency (DTMF) tones are the signals that are generated when you press a button on a touch-tone telephone.  This includes most of the commonly available phones. When the tone is generated, it is compressed, transported to the other party, and then decompressed.

DTMF Modes

There are 4 modes to select from. These are:

·         Inband
·         Outband (RFC2833)
·         SIP INFO (cisco format)
·         SIP INFO (Nortel format)

To change DTMF modes go to “VoIP>>Phone Settings”.

When selecting OutBand (RFC2833), you will need to select the “Payload Type”. The default setting is 101. This is the most common setting used, but can be changed to suit the ISP you are connected to.

What is the Difference Between InBand and OutBand?


This is the default setting in Vigor routers. In this mode during an active phone call any key pressed on the phone will be sent as regular sound along with your voice. The Vigor router will not process it. Since InBand treats the tones from key presses like normal audio it may not always be usable. When the audio stream is decompressed by your provider, the tone may have become distorted due to compression artifacts, lost packets, line jitter etc. This may make the tone unusable


When using Outband, special IP packets are generated and sent along with your voice when a key is pressed on the phone.  (For example if you press digit “2” on the phone, instead of sending an audible tone for “2” along with your voice, a special IP packet is generated.) These packets use RFC 2833 format, and must have a “payload type” that matches what the other end is listening for. The default setting is 101. At the receiving end, the special IP packets will be used to regenerate the pressed keys into the correct tone. Out of band is the best choice. It is useful on congested/distant or low quality calls.

Why key Presses are not recognised?

Most automated voice services will require you to press buttons on your phone to allow you to navigate the menus.  If the incorrect DTMF mode is selected in VoIP>>Phone Settings” then the key presses may not be recognised. Most services will use Inband but digital services may require OutBand to be used.