Silence detection

VoIPmonitor is able to detect (currently only for G711a/b) silence in RTP streams. Silence threshold is hardcoded in the code (it is tolerant to a little noise). It must be enabled in voipmonitor.conf (silencedetect = yes). When enabled following metrics are produced:

• Number of absolute silence audio frames (with 20ms length) which are treated as packet loss. On the following picture see the holes in the first audio stream - this example is taken from a call where RTP stream is coming without any packet loss or jitter, those audio drops are encoded directly in the RTP audio stream. With silencedetection = yes feature voipmonitor will calculate number of those silence frames and counts them as packet loss and calculates MOS score.

The MOS score is shown in the Graph in CDR detail as new MOS value "Sil" - see the RED 2.8 number

• Another silence feature is overall percentage of silence in each direction of a call which will be shown in cdr detail. Calls with >95% percent of a silence would indicate problem.

• number of silence seconds from the end of the last RTP packet - this might be the reason why someone hanged up the call because although RTP packets were coming, there was a silence. If value is non zero it will be shown also in CDR summary:

• Number of clipped frames (clipped frame has the highest volume) - perceived as audible clicks - this value is shown in cdr detail table. It can be filtered and used in charts

Data series in charts for silence, silence end and clipped frames.