As of LCOS version 9.20, a selection of DTMF signaling options is available for the transmission of DTMF tones over All-IP connections.
Settings for the DTMF signaling can be performed via the SIP line configuration and the SIP user configuration.
- DTMF signaling
- Depending on the requirements, it may not be sufficient to transmit "inband" DTMF tones if a SIP receiver cannot recognize these. In this case, it is possible to configure an alternative method of DTMF transmission for All-IP connections.
- Only in-band (in audio)
- The tones are transmitted as DTMF tones (G.711) in the RTP (voice) stream.
- Only SIP info
- The DTMF tones are transmitted "out-of-band" as a SIP-info message with the parameters Signal and Duration (as per RFC 2976). There is no parallel transmission of G.711 tones.
- Telephone events - fallback to in-band (default)
- The DTMF tones are transmitted as specially marked events within the RTP stream (as per RFC 4733). There is no parallel transmission of G.711 tones. If the call-initialization SDP message does not include telephone-event signaling, negotiations fallback to inband transfer as per G.711.
- Telephone events - fallback to SIP info
- The DTMF tones are transmitted as specially marked events within the RTP stream (as per RFC 4733). There is no parallel transmission of G.711 tones. If the call-initialization SDP message does not include telephone-event signaling, negotiations fallback to transfer as per SIP-Info message.