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2560 CHAPTER 173: VOIP CONFIGURATION COMMANDS
g729r8: G.729 (the voice compression technology using conjugate
algebraic-code-excited linear-prediction), requiring a bandwidth of 8 kbps.
Description Use the
compression command to configure the voice compression method and
the preference level.
Use the
undo compression command to restore the default value.
By default, the codec with the first priority is g729r8, that with the second priority
is g711alaw, that with the third priority is g711ulaw, and that with the fourth
priority is g723r53.
g711alaw and g711ulaw provide high-quality voice transmission, while requiring
greater bandwidth.
g723r53 and g723r63 provide silence suppression technology and comfortable
noise, the relatively higher speed output is based on multi-pulse multi-quantitative
level technology and provides relatively higher voice quality to certain extent, and
the relatively lower speed output is based on the Algebraic-Code-Excited
Linear-Prediction technology and provides greater flexibility for application.
The voice quality provided by g729r8 and g729a is similar to the ADPCM of 32
kbps, having the quality of a toll, and also featuring low bandwidth, lesser event
delay and medium processing complexity, hence it has a wide field of application.
Table 664 describes the relationship between codec algorithms and bandwidth.
Actual network bandwidth is related to packet assembly interval and network
structure. The longer the packet assembly interval is, the closer the network
bandwidth is to the media stream bandwidth. More headers consume more
bandwidth. Longer packet assembly interval results in longer fixed coding latency.
The following tables show the relevant packet assembly parameters without IPHC
compression, including packet assembly interval, bytes coded in a time unit, and
network bandwidth, etc. Thus, you can choose a suitable codec algorithm
according to idle and busy status of the line and network situations more
conveniently.
Table 664 Relationship between algorithms and bandwidth
Codec Bandwidth Voice quality
G.711 (A-law and µ-law) 64 kbps (without compression) Best
G.726 16, 24, 32, 40 kbps Good
G.729 8 kbps Good
G.723 r63 6.3 kbps Fair
G.723 r53 5.3 kbps Fair