3Com NBX 100 Administrator's Manual - page 38
38
C
HAPTER
2: S
YSTEM
S
ETTINGS
Codec Selection
It is important to remember not to select a codec based on compression
alone. Consider the trade-off between audio quality and bandwidth use.
System-Wide Audio
For system-wide audio, base the default list order on audio quality:
VTL Calls Audio
For Virtual Tie Line (VTL) audio, base the default list order on bandwidth
usage:
G.722
G.722.2
G.722.2LB
Wideband Audio
G.722.2 is an ITU-T standard for wideband voice applications and
services. G.722.2 is an adaptive multi-rate wideband codec that
uses bit rates ranging from 6.6 to 23.85 kbps.
G.722 is an SB-ADPCM (sub band Adaptive Pulse Code
Modulation) codec. It runs ADPCM on both the low band (0 -
4000 Hz) and the high band (4000 - 8000). The raw bit rate
(without network packet headers) is 64 kbps.
G.722.2 is a CELP (code excited linear prediction) based codec.
G.722 is a 23.85 kbps rate. G.722.2 LB has a rate of 8.85 kbps.
The standard was originally designed for wireless networks and
the different rates allow for adapting to varying channel
conditions.
Table 7 Supported Codecs
Codec
Description
Table 8 Default Order List Based on Audio Quality
Codec
Quality
Bandwidth
G.722.2
best quality
medium bandwidth
G.722
high quality
high bandwidth
G.711
good quality
high bandwidth
G.722.2LB
good quality
low bandwidth
G.729
medium quality
low bandwidth
ADPCM
low quality
medium bandwidth
Table 9 Default Order List Based on Bandwidth Usage
Codec
Quality
Bandwidth
G.722.2LB
good quality
low bandwidth
G.729
medium quality
low bandwidth