DTMF in-band means DTMF tones are sent as audible tones along with the voice (DTMF is sent IN the voice frequency BAND).
DTMF out-of-band means DTMF tones are sent as the numerical value in a packet (RTP type telephone-event, refer RFC2833).
High-compression codecs such as G.729 are designed to carry voice waveforms not tones, so may have problems with DTMF in-band.
You can set your VOIP device either way. Whether out-of-band works depends on your provider also supporting it.
DTMF out-of-band means DTMF tones are sent as the numerical value in a packet (RTP type telephone-event, refer RFC2833).
High-compression codecs such as G.729 are designed to carry voice waveforms not tones, so may have problems with DTMF in-band.
You can set your VOIP device either way. Whether out-of-band works depends on your provider also supporting it.
