Voice over IP (VoIP) | Fundamentals |
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The following comparison provides a guide to voice quality with specific quality levels:
Quality Levels for Voice Transmission with VoIP
Level | Voice Comprehensibility | Comparable to |
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1 | Very Good | ISDN |
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2 | Good | DECT |
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3 | Satisfactory | GSM |
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4 | Limited | Defective GSM |
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> 4 | Unacceptable | No Connection |
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When a call is set up, the terminals involved negotiate the
■G.711
■G.729A (Level 2): Reduction to approximately 8 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
■Duration > 60 ms: two
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
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