Subjective evaluations of IP telephony were collected while network performance was varied using an IP network emulator. Packet loss was set at 0%, 1%, or 8%. Mean one-way delay was set at 8 ms, 46 ms, or 156 ms (in addition to system delay of 90 ms). Delay variation (standard deviation) was set to 1 ms, 8 ms, or 17 ms. For combinations of these network settings, a standard mean opinion score (MOS) of speech quality was collected from 31 human judges. MOS is reported as a function of the network emulator settings.
Gregory W. Cermak,
"Speech quality as a function of IP network performance", Proc. SPIE 3845, Multimedia Systems and Applications II, (22 November 1999); doi: 10.1117/12.371192; https://doi.org/10.1117/12.371192