ITU-T recommendation G.107 describes a model for transmission planning called the E-model. The E-model combines a number of different impairments to calculate an overall quality measure, R.
R = Ro – Is – Id – Ie + A
The R factor ranges between 0 and 100, 0 being the worst and 100 the best.
- Ro is the signal to noise ratio including background noise and transmission noise
- Is represents the simultaneous impairment factor
- Id represents impairment caused by delay
- Ie is the equipment impairment factor representing impairments from low-bit codecs and packet loss
- A is the advantage factor, which is a compensator to off-set the others. For example using a DECT handset or a mobile phone gives user mobility advantages which off-set the impairment caused by (for example) errors in the radio interface
Mean opinion score (MOS) is a test used to obtain the human user’s view of the quality of the network. It ranges from 1 to 5, 1 being the worst and 5 the best.