Knowledgebase: Voice over Internet (VoIP)
What DTMF Mode should I use?
Posted by Gabriel Yu on 11 April 2008 07:09 AM
What is DTMF (Dual Tone Multi Frequency) ?|
When you press a button on your phone it sends a combination of two audible tones (identifying the column and row of the key on the standard keyboard layout), which can be separated at the other end to determine which key you pressed.Â Also known as touch-tone.
DTMF tones are used for dialling a phone number, and also when you respond to an IVR (Interactive Voice Response) system, such as are becoming increasingly common for telebanking, voicemail, and automated receptionists (press 1 for sales, 2 for technical ...).
What are the DTMF modes ?
On a standard PSTN phone line, the DTMF tones are always sent as part of the audio data (InBand); but the higher compression from VoIP codecs (which are designed for speech, not data tones) means that codec at the other end cannot be guaranteed to reproduce these tone signals accurately enough for automatic recognition.
VoIP offers a variety of possibilities, such as:
Which DTMF mode should I use ?
If all your calls are to PSTN numbers, then find out from your VoIP provider which DTMF mode their PSTN Gateway uses, and set you VoIP device to the same setting.
Unfortunately some customers find that different systems require different DTMF modes (e.g. the VoIP providers voicemail may require SIP INFO, but the customer needs to use InBand for their telebanking).