Voice Quality - Aastra 800 User Manual

Voice over IP (VoIP)
An IP packet consists of protocol data and user data. Sending shorter voice-data
packets causes the ratio between the user data and the protocol data to become
unfavourable and increases the bandwidth required. Sending longer voice-data
packets increases latency.
The length of the voice-data packets must therefore be adjusted to the require-
ments of the transmission medium. Shorter voice-data packets can be sent if a
direct ethernet connection exists. If an 64 kbit/s ISDN line is to be used for trans-
mission, then longer voice-data packets should be used.
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.
Required bandwidth (kbit/s) with respect to Packet Length and Codec
Packet Length (ms)
20
30
40
50
60
70
80

7.2.3 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.
G.711 (not compressed) G.729A approx. 8 kbit/s
180.8
Fundamentals
68.8
51.2
42.4
37.12
33.6
31.09
29.2
63