Mean Opinion Score (MOS) is a numeric representation of the audio quality of a call, taking a value between 1.0 (worst) through 5.0 (best). It is a subjective measurement; a good MOS depends on the codec. For example, for G711 and G722, the top score is 4.5. For G729, the top score is 3.9.
The
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MOS value is assigned to every call and for each direction of the call. This value is calculated by a mathematical formula that approximates real MOS scores. It is calculated using 10-second snippets of audio. The worst-case 10-second period is logged at the end of the call.A logging record is added to the VOS log file every time a call is started and terminated (and sometimes mid-call). The log file can be viewed from the Admin > System Information page. Refer to View System Information.
MOS scores are measured when the audio (RTP) stream reaches the
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. The scores calculated by the Unable to show "metadata-from": No such page "_space_variables"
make certain approximations:- The same call (RTP stream) can sound different on different VoIP phones. Some phones do better than others at hiding errors in a stream. The MOS score, however, will be the same regardless of the endpoint. So a given score can sound better or worse depending on the endpoint in use.
- The user may not notice a momentary packet loss in a stream, but such a loss might result in a low MOS score. A single low MOS score should not be assumed to mean poor quality for the user. A pattern of low scores across multiple calls is more significant.
What to look for in a low score:
- For outbound scores (VOIP phone to Network), this is a measurement of the handset and intervening local area network. A low score in this direction can mean a handset or network issue.
- For inbound scores (Network endpoint to VoIP phone), this is a measurement of the originating endpoint and full WAN path.
Overview
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