How it is calculated
The E-model from ITU-T G.107 starts at R = 93.2 and subtracts impairments: for mouth-to-ear delay (network, jitter buffer, packetization, codec look-ahead) and for the codec together with packet loss. R maps to MOS on a 1 to 4.5 scale. It is a planning estimate, not a measurement of a real call; to measure a real call, use the pcap analyzer.
| Network | R | MOS |
|---|---|---|
| Metro fibre: 10 ms, 2 ms jitter, no loss, G.711 | 92 | 4.38 |
| Long distance: 60 ms, 10 ms jitter, 0.5% loss, G.711 | 89 | 4.31 |
| Mobile data: 80 ms, 30 ms jitter, 2% loss, G.729 | 70 | 3.60 |
| Satellite: 280 ms, 20 ms jitter, 1% loss, G.711 | 64 | 3.28 |
What matters most
Packet loss: even 2–3% audibly hurts, especially for codecs without packet loss concealment (PLC). Up to 150 ms one-way delay is barely noticed; beyond 250–300 ms people start talking over each other. Jitter itself is not heard, but it grows the jitter buffer and so the delay; with too small a buffer, jitter turns into loss.