DTMF Recongnition Failure in IVR due to Payload Negotiation Failure


  • Firmware version: Any
  • Model: S-series PBX

Problem Description

Calls from different mobile phones to IVR in PBX through SIP trunk then press DTMF key as prompt to reach expected destination. However some mobile phone could not reach the correct destination.


As per pcap file captured from failed call. It could be seen the payload 101 before telephone-event in the SDP of provider's INVITE packet. However the PBX will read it and take it as payload of telephone-event and ignore the real payload 105 and 106 after 101.



Contact the SIP provider to remove AMR-WB in its SDP of INVITE packet.

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