R-Factor vs MOS Score in VoIP Quality
R-Factor and MOS code are quality measurement in VoIP. In circuit switching in TDM world a channel will be dedicated for a call until the call releases. But in the IP world packet networks are shared by many users and many applications. Lots of parameters will affect the VoIP quality on packet networks such as packet loss, packet delay variation (Jitter), out of order delivery. However measurements of these individual parameters will not define the end to end or leg to leg quality of the calls.
R-Factor (E-Model)
R-Factor is one way of measuring the VoIP quality in IP networks. This value is derived from couple of parameters like delay and network impairments. R-Factor ranges from 0 (Extremely poor quality) to 100 (High Quality). Any R-Factor less than 50 is not acceptable. TDM based phone calls have R-Factor of 94. There are 3 main variations of R-Factors they are R-Call Quality Estimate, R-Listening Quality Estimate and R-Network Performance Estimate.
R-Factor = Ro-Is-Id-le eff – Irecency +A
Where Ro – Signal to Noise Ratio (SNR), Is – Combination of all impairments that occur simultaneously with the voice signal, Id – Impairment caused by delay, Ie eff – Impairments caused by a low bit rate CODECs , Irecency – Impairment caused by packet loss and A – Advantage factor
MOS
MOS (Mean Opinion Score) is another method of measuring VoIP quality. MOS value measures quality of voice over IP network considering account into both CODEC and network impairments. MOS code ranges from 1 (Bad) and 5 (Excellent). MOS score is calculated by complicated algorithms based on ratings from large groups of listeners. MOS score can be increased by PLC (Packet Loss Control) algorithms. Most vendors these days use algorithms to mask the packet loss by introducing multiple same packet transmission and regenerating the same packets at the receiving 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 |
Summary:
(1) R-Factor and MOS score both are ways of measuring the quality of voice in VoIP systems.
(2) R-Factor and MOS calculated by parameters like delay, Jitter, packet loss but MOS score calculations get inputs from user ratings as well.
(3) R-Factor ranges from 0 to 100 and MOS score ranges from 0 to 5.
(4) If MOS Score is more than 3.1 and R-Factor is more than 70 is rated as a good call.