DETEWE OpenCom 130 - Page 105

Voice over IP (VoIP) Fundamentals
103
■ G.729A (Level 2): Reduction to approximately 8 kilobit/s.
■ G.723.1 6.3 (Level 3): Reduction to 6.3 kilobit/s.
■ G.723.1 5.3 (Level 3): Reduction to 5.3 kilobit/s.
Unfavourable packet length selection may reduce voice quality. The duration of
the recording and not the data packet’s byte count is relevant in making this
selection:
■ Duration <= 30 ms: optimal transmission
■ Duration 40 - 60 ms: one quality-level depreciation
■ Duration > 60 ms: two quality-levels depreciation
The achievable voice quality also depends on the packet propagation delay and
the packet loss between the terminals involved. These parameters can be deter-
mined using the “ping” program.
Note: Measurements made with “ping” are round-trip pro-
pagation delays. Divide the maximum value displayed by
two.
Packet Propagation Delay and Packet Loss
Value Quality Level Value Quality Level
Propagation delay
< 50 ms
Optimal Loss < 1 % Optimal
Propagation delay
50-100 ms
0.5 level
depreciation
Loss 1-2 % 0.5 level
depreciation
Propagation delay
100-150 ms
1 level
depreciation
Loss 2-3 % 1 level
depreciation
Propagation delay
150-200 ms
2 level deprecia-
tion
Loss 3-4 % 2 level
depreciation
Propagation delay
200-300 ms
3 level deprecia-
tion
Loss 4-6 % 3 level
depreciation
Propagation delay
> 300 ms
4 level deprecia-
tion
Loss > 6 % 4 level
depreciation