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MOS is a numerical system used to grade the subjective perceptual quality of a multimedia (audio, video, or both) user experience.

Originally based on ITU-T recommendations for the evaluation of voice quality, it uses a scale of 1 - 5 to indicate user experience with the following typical benchmarks:

 

5 Excellent Imperceptible. No degradation of quality can be detected by a human subject.

4 Good Perceptible. Degradation can detected, but does not adversely impact the user   experience.

3 Fair Slightly annoying

2 Poor Annoying

1 Bad Very annoying or no data stream present

 

MOS scoring is frequently produced by software algorithms that monitor multimedia streams and attempt to “emulate” a subjective user experience. Such software is intended to produce results that are similar to MOS scores that would be recorded by actual human participants consuming and evaluating the media.

 

The R-factor is a similar concept and is actually the mathematical component by which a MOS is estimated. It is calculated using what is known as the “E-model” formula. This formula involves a subjective summation of impairment and “advantage” factors, including the typical packet network parameters such as jitter, latency, and loss. Like the MOS score, the higher the number, the better. An R-factor result is presented as a percentage, where 80% loosely corresponds with an MOS score of 4, and a factor of 50% corresponds with an MOS of 2.6.

 

While these types of measurement may help you view a snapshot summary of network quality, you should remember that “real,” quantifiable network conditions are the only reliable means of judging network integrity. Any means of numerically calculating the quality of the human experience is necessarily subjective.