DTMF from Mobile Detection Failure due to the Mobile Audio Coding


  • Firmware version: Any
  • Model: TGv2, Module - SIM800

Problem Description

The call flow is like this: Mobile phone->TG gateway->SIP trunk->PBX->IVR. When mobile phone caller pressed extension number as prompt, while the expected extension didn't ring.



In PCAP capture file from TG to pbx for same call flow, the DTMF waves were sent incompletely, last DTMF was missing. So problem is on TG gateway side. This is possible TG didn't detect it as a normal DTMF and send it to PBX though it is received so we need to figure out how to improve the opportunity to detect the last one as a normal DTMF in gateway.


As per channel recording for designated GSM port, gateway already received 3 DTMF waves. But the 3rd one is not standard for DMTF frequency.



For TGv2 gateway, we could try to set the audio coding negotiation to improve the voice quality (DTMF Wave).

Mostly you can try the SVR value 0 or 1. The codec represents the best voice quality codec for mobile. The default SVR value is 16.

The command executed in the GSM module debug mode is:

gsm send at 2 at+svr=1

Also refer the value mapping for SVR.



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