The quantitative assessment of the quality of VoIP communication is often measured by its MOS score (Mean Opinion Score). The MOS score ranks the quality based on a number in the range of 1 to 5.
The original idea behind the MOS score was to take the mean average of all the individuals rating the quality of a test call. That soon changed, as modern network analyzers have the ability to calculate MOS score using artificial software algorithms.
The MOS score is highly subjective and should not be used as the deciding factor in a VoIP system deployment. Other measures should also be taken into consideration such as packet loss, jitter, latency, etc.
The R-Factor is calculated by evaluating user perceptions as well as the objective factors that affect the overall quality of a VoIP system, accounting for the Network R-factor and the User R-factor separately.
The R-Factor uses both a Network R-Factor along with a User R-Factor to to calculate the overall quality of voice. The Network R-Factor is based on the equipment impairments, (Latency, packet loss, jitter, etc). The User R-Factor attempts to add the “perceived” annoyance a user may experience during a call. The perceptual effect is called recency. Recency or short term auditory memory can greatly affect the perceived quality of voice.
|R-Factor||MOS Score||User Experience|
|90 - 100||4.3 – 5.0||Excellent|
|80 - 90||4.0 – 4.3||Good|
|70 - 80||.6 – 4.0||Fair|
|60 - 70||3.1 – 3.6||Poor|
|50 - 60||2.6 – 3.1||Bad|
A network analyzer can be used to collect the R-Factor, MOS score, packet loss, latency and jitter measurements. NETSCOUT OneTouch AT has the ability to do inline VoIP analysis.