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Fundamentals
156
Voice over IP (VoIP)
Longer voice data packages are generally used for SIP telephony over the
Internet.
The following table provides an overview of the required bandwidth for a
telephone connection with various parameter settings. The values apply to
half-duplex ethernet; for full-duplex the values can be halved.
Voice Quality
The achievable voice quality depends on various factors. It is possible to
optimise voice-data transmission on an existing network using the available
configuration settings. Measuring the network quality may also help.
The following comparison provides a guide to voice quality with specific
quality levels:
Required bandwidth (kbit/s) with respect to packet length and codec
Packet length (ms)
G.711
(not compressed)
G.729A
approx. 8 kbit/s
20
180.8
68.8
30
51.2
40
42.4
50
37.12
60
33.6
70
31.09
80
29.2
Quality levels for voice transmission with VoIP
Level
Voice comprehensibility
Comparable to
1
Very Good
ISDN
2
Good
DECT
3
Satisfactory
GSM
4
Limited
Defective GSM
> 4
Unacceptable
No Connection
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