VoIP glossary · Mean Opinion Score
What is MOS?
MOS (Mean Opinion Score) is a 1-to-5 rating of perceived call quality, where 5 is excellent and anything above about 4 sounds like a normal phone call.
MOS explained
MOS originally came from panels of listeners scoring recordings. Today most systems estimate it from network measurements, combining latency, jitter, packet loss and the codec in use. G.711 on a clean network typically scores around 4.3, while G.729 scores slightly lower even in perfect conditions.
Because it is an estimate, MOS is best used to compare calls on the same system over time. A drop from 4.2 to 3.5 on one route is a clear signal; a single score in isolation tells you less.
Example
A monitoring dashboard shows MOS falling to 3.2 every afternoon. The cause turns out to be backups saturating the office uplink at 3 p.m.
Put it into practice
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