How Is VoIP MOS Calculated?
Let me explain how the Mean Opinion Score (MOS) for VoIP is calculated. MOS is a measure used to evaluate the quality of voice calls in VoIP systems. It is a score typically ranging from 1 to 5, where 5 represents excellent quality, and 1 indicates poor quality. MOS helps to quantify the subjective quality of the voice service as experienced by the user.
Factors Influencing MOS
Several factors impact the MOS score in VoIP, including:
- Latency: Delay in transmission can lead to poor call quality. Higher latency results in echoes and delays in conversation.
- Packet Loss: Loss of voice packets during transmission can lead to audio gaps or distortion, lowering the MOS score.
- Jitter: Variability in packet arrival times can cause uneven audio quality, which impacts MOS.
- Bandwidth: Insufficient bandwidth can cause voice data to be compressed, leading to lower audio clarity and poor MOS scores.
How Is MOS Calculated?
MOS can be calculated using both subjective and objective methods:
- Subjective Method: This involves human testers who listen to voice calls and assign a score based on their perception. However, this is impractical for large-scale evaluations.
- Objective Method: This is the more commonly used method, where MOS is calculated based on network performance metrics like packet loss, jitter, and latency. A commonly used formula to calculate MOS is based on the ITU-T P.800 standard, which defines the relationship between network impairments and voice quality.
Common Formula for MOS
One of the widely used formulas for estimating MOS in VoIP is the E-model, as defined by ITU-T. The formula looks like this:
MOS = 1 + 0.035 * I + 0.000007 * I^2
Where I is the impairment factor that combines various network issues such as delay, jitter, and packet loss.
Practical Example
For example, if the impairment factor (I) is 50, you would calculate the MOS as:
MOS = 1 + 0.035 * 50 + 0.000007 * 50^2 = 4.0
This would suggest a good quality call, but not the best. The higher the MOS, the better the call quality, with 5.0 representing the highest quality.
So, in short, MOS is calculated based on network conditions and voice call quality, with objective methods like the E-model being the most common way to estimate it in VoIP systems.