Quality of Service
BAT54-Rail/F..
Release
7.54
06/08
9.5
QoS parameters for Voice over IP applica-
321
In case of a delay of not more than 100 ms, and a packet loss of less than
5%, the quality is felt like a “normal” telephone connection. In case of more
than 150 ms delay and less than 10% packet loss, the telephone user per-
ceives still a very good quality. Up to 300 ms and 20%, some listeners feel
this quality like still suitable, beyond that the connection is considered as no
more suitable for voice transmission.
Apart from the average delay time, also a variation in this delay is perceived
by the human ear. Delay differences of the voice information from sender to
addressee (jitter) are still tolerated up to 10 ms, and values beyond consid-
ered as irritating.
Accordingly, a VoIP connection should be configured such that the criteria for
good speech quality are met: Packet loss up to 10%, delay up to 150 ms and
jitter up to 10ms.
D Jitter can be removed in the receiving station by an appropriate buffer. In
this buffer (jitter buffer) the packets are stored intermediately, and passed
on at a constant rate to the addressee. By this intermediate buffering, the
delay variations due to individual transmission times of the individual
packets can be removed.
D The delay is influenced by several components:
For BAT devices with VoIP functions that were already integrated or added
in with a software option, the QoS settings for SIP calls are defined auto-
matically.
Packet loss Jitter
Delay300 ms150 ms100 ms
20 %
5 %
10 %
10 ms
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