R-Factor vs. MOS Score in VoIP Quality

Difference between R-Factor and MOS Score in VoIP Quality

R-Factor and MOS code are two means by which VOIP quality is measured. Packet loss, out of order delivery, packet delay variation and many other parameters are there which will determine the VOIP quality. But the quality of a VOIP call from the start to the termination can never be defined by any one parameter.

R-Factor (E-Model)

R-Factor is just one way by which the VoIP quality in IP networks can be measured. Delay and network disabilities are some of the factors which help to determine the value of R-Factor. This value ranges from 0 (which means extremely poor quality) to 100 (meaning High Quality). Any R-Factor which will have lesser value than 50 is not accepted. Phone calls which are based on TDM have R-Factor value of 94. are R-Call Quality Estimate, R-Listening Quality Estimate and R-Network Performance Estimate are three main variations of R-Factors.

R-Factor = Ro-Is-Id-le eff – Irecency +A


  • Ro – Signal to Noise Ratio (SNR),
  • Is – Combination of all the disabilities that takes place simultaneously with the voice signal,
  • Id – Disabilities which are caused by delay,
  • Ie eff – Disabilities caused are by a low bit rate CODECs ,
  • Irecency – Disabilities caused by loss of packets and
  • A – Advantage factor


Another means of measuring VoIP quality is MOS (Mean Opinion Score). MOS value is all about the measures quality of voice over IP network taking account disabilities of both CODEC and network. The value of MOS code varies from 1 (Bad) and 5 (Excellent). MOS score is calculated by complicated algorithms which are based on the ratings that are given by a huge database of listeners. PLC (Packet Loss Control) algorithms are one way of increasing MOS value. Algorithms are used nowadays to mask the packet loss by introducing multiple same packet transmission and regenerating the same packets at the recipients’ end.

User Satisfaction Level MOS R-Factor
Maximum using G.711 4.4 93
Excellent 4.3 – 5.0 90 -100
Good 4.0 – 4.3 80  – 90
Satisfied 3.6 – 4 to – 80
Dissatisfied 3.1 – 3.6 60 -70
Fully Dissatisfied 2.6 – 3.1 50 -60
Not recommended 1.0 – 2.6 Less than 50




  • Values of R-Factor are determined by factors like delay, packet loss and jitter.
  • Range of value R-Factor is from 0 to 100
  • A good VOIP call will have a R-Factor more than 70


MOS score

  • Values of MOS score are determined by factors like delay, packet loss and jitter. However inputs from user ratings are needed as well.
  • MOS score ranges from 0 to 5.
  • A good VOIP call will have a MOS score of more than 3.1