Setting up and using the DTMF keypad on Telegram calls

To open the DTMF keypad during a call, swipe the screen up or left, or press the Back button. Keypad is sent to chat with user @siptg (in Softphone mode) or to chat with gateway account where call history is contained (in Gateway mode).

When configuring SIP-accounts from some service providers or registration from PBX, whose settings are not in our list of Server Templates, you may need to manually specify one of three methods of DTMF keyboard operation: RFC2833, inband and INFO (all methods, except inband, send confirmation).

RFC2833 is the primary method of transmitting push-button signals in SIP networks. However, because of the freedom in implementation, some systems are incompatible with each other (in this case there are INFO and inband methods).

Inband is when the tone signal of the button press is transmitted in a common stream with the voice, but because of the audio codecs used it can be distorted and the receiving side does not recognize it. Therefore this method is usually used only as a last resort.

INFO is one of the newest means of DTMF transmission. On the one hand, the method is quite reliable and easier to implement than RFC2833, but not all operators support it due to its novelty.

The required value is specified without spaces, case insignificant.