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Collaboration, Voice & AV · Foundational

Mean Opinion Score (MOS)

A 1-to-5 rating of perceived voice or video quality, where 5 is excellent and about 4 or higher is toll quality.

Definition

MOS was originally derived from listener panels (ITU-T P.800) and is now commonly estimated by algorithms such as the E-model (G.107) R-factor, PESQ or POLQA. G.711 typically scores about 4.1 and G.729 about 3.9. Collaboration tools such as Webex Control Hub and the Teams Call Quality Dashboard report estimated MOS for calls.

Example

A call with 2 percent loss and 200 ms delay has a computed MOS of 3.3, flagged as poor in the analytics dashboard.

Exam tip

Toll quality is roughly MOS 4.0; know the relative MOS values of G.711 versus compressed codecs.

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