Voice over IP (VoIP)
113
•
G.711
A-Law or µ-Law (Level 1, uncompressed): The audio data of a PCM channel
(64 kbit/s) is adopted one-to-one. Every VoIP terminal must support this codec.
This codec can not be used with an ISDN data connection.
•
G.729A
(Level 2): Reduction to approximately 8 kbit/s.
•
G.723.1 6.3
(Level 3): Reduction to 6.3 kbit/s.
•
G.723.1 5.3
(Level 3): Reduction to 5.3 kbit/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 determined
using the “ping” programme.
Note
Measurements made with “ping” are round-trip propagation 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
depreciation
Loss 3-4 %
2 level depreciation
Propagation
delay 200-300 ms
3 level
depreciation
Loss 4-6 %
3 level depreciation
Summary of Contents for OpenCom 100 series
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