Aastra Telecom 800 User Manual
Voice over IP (VoIP)
Fundamentals
63
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.
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.
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.
phone connection with various parameter settings. The values apply to half-
duplex ethernet; for full-duplex the values can be halved.
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.
voice-data transmission on an existing network using the available configuration
settings. Measuring the network quality may also help.
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