Configuring DTMF

You can use the dual-tone multi-frequency (DTMF) properties to configure DTMF event handling.

Vocera SIP Telephony Gatewaysupports dual-tone multi-frequency (DTMF) signaling. You can press keys on your phone to send DTMF tones to the PBX. The DTMF signaling is transmitted in the RTP stream, but it is not encoded as part of the audio; it is included as a separate payload type. The volume, duration, and inter-digit duration of DTMF signals are all configurable. You can also configure Vocera SIP Telephony Gateway to not hang up the call until all the DTMF digits are sent.

The DTMF digits supported are 0 through 9, #, or *. For arbitrary pauses in a secondary dial string, you can add comma and semicolon to the DTMF queue. When the RTP sending thread pulls a comma or semicolon off the DTMF queue, it will stop sending DTMF for as long as the character represents. The duration of comma and semicolon pauses is configurable for each trunk access code; see Configuring Trunk Access Codes (TACs).

The following properties let you configure handling of DTMF events:

Table 1. DTMF properties




Specifies the interval between DTMF digits in milliseconds. The default is 250.


Specifies the duration of each DTMF digit in samples. For G.711, the sampling rate is 8000 samples/second, which means each sample is 1/8000 second (0.125 milliseconds). The default value for VGWDTMFDuration is 900 samples (112.5 milliseconds).


Specifies the volume of DTMF signals in absolute dBm0 (the sign is removed). Enter a value between 36 and 0. The default is 16. If you enter a value outside the valid range, 16 is used.


Whether to not disconnect the call until all DTMF digits in the queue have been sent. The default is FALSE, that is, the call is hung up without waiting for DTMF digits in the queue.