Voice over IP (VoIP) Fundamentals
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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.
You will require a licence with which you can activate the G.729 codec for oper-
ation (in the System: Licences menu).
Note: To ensure SIP compatibility, the older system tele-
phones OpenPhone 63 IP and OpenPhone 65 IP do not sup-
port the G.723 codec any more.
9.2.3 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
1Very Good ISDN
2Good DECT
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