Difference Between R-Factor and MOS Score

R-Factor vs MOS Score in VoIP Quality

VoIP has made it possible to make calls relatively cheap no matter the distance between you and the person you are calling. But along with the benefits there are disadvantages. Call quality is often problematic especially when the connection is not reliable. In order to improve the user experience, mechanisms for measuring call quality, like R-factor and MOS score, were created. The main difference between the MOS score and R-factor is the testing process. R-factor is an objective measurement that is based on several factors like signal to noise ratio. In comparison, as clearly implied by its name, MOS (Mean Opinion Score) is a subjective test that is based on user perception rather than on measurable statistics. Scores are collated from multiple people participating in the test and the mean is taken.

Although the results of both can be correlated with each other, there is a wide discrepancy in the scales they use. R-factor uses a scale of 0-100 while MOS uses a scale of 1-5. Obviously, both scores would match at the top and at the bottom. But for a passing score, you need an R-factor of about 70 or a MOS score of around 3.6; scores of over 80 and 4.0 respectively mean highly satisfactory systems.

Although both measurements are quite useful, R-factor is a more realistic procedure as it can be tested under normal circumstances. In order to obtain a meaningful MOS score, the tests needs to be conducted under controlled conditions. The MOS score is often used to test the different codecs, which are used to compress the voice data. Compression is often lossy but it is necessary in order to reduce the bandwidth consumption and squeeze more conversations into a given medium. Some codecs are better than others in reducing bandwidth requirements while still retaining call quality. The MOS score is a great tool in gauging the response of real people to the compression level and call quality.

Summary:
R-factor is an objective test while MOS score is a subjective test
R-factor has a scale of 0-100 while the MOS score has a scale of 1-5
R-factor is a more realistic value than MOS score

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