MOS Scoring is a subjective test of a call quality originally designed by the Bell Companies to quantify the quality of a voice call; with 1 being unacceptable and 5 being superlative. MOS Scoring is also used by Codec and hardware designers to validate their technology during design.
A typical range for Voice over IP would be from 3.5 to 4.2 using a G.711 Codec. In contrast, a score of 2.8 to 3.2 is typically seen in cellular usage and the G.729 Codec.
- 1 = bad
- 2 = poor
- 3 = fair
- 4 = good
- 5 = excellent
MOS Scores are of particular importance when measuring the degradation of a call when voice call compression is used in different VoIP codecs such as G.729a where bandwidth conservation needs to be measured against resultant call quality degradation.
"Toll quality" sound is associated with a MOS score of at least 4. G.711 starts with a MOS score of 4.4. G.729, which performs compression, has an average MOS score of 4.1. With VoIP, the MOS score will be further reduced when there is packet loss, excessive delays, etc.
