Resolving Out-of-Band DTMF Issues in SIP Trunking

When it comes to SIP trunking, sending dual-tone multi-frequency (DTMF) tones can be a complex process. Some softphones may send both in-band and out-of-band DTMF signals, which can result in duplicate tones when the SIP proxy is configured to send the tone to Avaya in-band. In this scenario, between the SIP proxy and the CM G.711MU codec, it appears that the Avaya CM only detects in-band DTMF tones and fails to recognize out-of-band tones based on RTP payload (RFC 2833).

The SIP proxy can send DTMF signals both in-band and out-of-band, but neither option seems to work reliably with various softphones used on the SIP side. This includes WebRTC/JsSIP with Chrome and Firefox browsers. To further complicate matters, we have a SIP trunk established between a CM6 and a repro SIP proxy, and we are struggling to get DTMF detection working reliably for SIP-to-Avaya calls.

To resolve this issue, it is essential to understand the nuances of DTMF signaling in SIP trunking. In-band DTMF tones are transmitted within the audio stream, while out-of-band tones are sent as separate RTP packets. The Avaya CM seems to only detect in-band tones, which can lead to issues with DTMF detection.

One potential solution is to configure the SIP proxy to use a specific codec that supports both in-band and out-of-band DTMF signaling. This may require modifying the configuration settings of the SIP proxy or the softphones used on the SIP side.

Another approach is to investigate alternative methods for sending DTMF signals, such as using SIP INFO messages or modified RTP packets. This could involve working with the SIP proxy and the Avaya CM to develop a custom solution that meets the specific requirements of your setup.

Ultimately, resolving out-of-band DTMF issues in SIP trunking requires a deep understanding of the technical nuances involved. By working closely with your SIP proxy and softphone vendors, you can develop a reliable solution for detecting DTMF tones and ensuring seamless communication between your SIP trunk and Avaya CM system.

Out of band dtmf