Fundamentals
Voice over IP (VoIP)
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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 tele-
phone connection with various parameter settings. The values apply to half-
duplex ethernet; for full-duplex the values can be halved.
Note:
To ensure SIP compatibility, the older VoIP system telephones
do not support the G.723 codec any more.
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
G.723.1
6.3 kbit/s
G.723.1
5.3 kbit/s
20
180.8
68.8
30
51.2
48.0
45.9
40
42.4
50
37.12
60
33.6
30.4
28.3
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