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Voice quality network requirements
Table 41: Comparison of speech coding standards
(without IP / UDP / RTP overhead)
Because it does not use compression, G.711 offers the highest level of voice quality.
Unfortunately, there is a trade-off with higher bandwidth usage. In situations where bandwidth is
scarce, such as across WAN links, G.729 offers a good compromise with lower bandwidth
usage, but still good fidelity audio.
Compression codecs use twice as many DSP (digital signal processor) resources than the
G.711 codec. Each call using a compression codec uses two DSP resources - one for sampling
and one for the compression. On the TN2302AP (MedPro) circuit pack (and on the G700 VoIP
engine) there are 64 DSP resources. Thus, the number of calls supported by one MedPro or
G700 is:
64 G.711 calls
32 compressed calls (for example, G.729)
Some number in-between for a call mix.
The formula for calculating the number of calls one MedPro supports is
Number of uncompressed calls
Generally, G.711 is used within LANs because bandwidth is abundant and inexpensive whereas
G.729 is used across WAN links because of the bandwidth savings and adequate voice quality.
212 Avaya Application Solutions IP Telephony Deployment Guide
Standard
Coding Type
G.711
PCM
G.729
CS-ACELP
G.723.1
ACELPMP-MLQ
1. As predicted. Measured according to ITU-IT Recommendation P.862
(PESQ). See draft Recommendation P.862.2, application guide for PESQ.
2. Given MOS-LQO values for American English.
Bit Rate
(kbps)
64
8
6.3
5.3
+
2
Number of compressed calls
1
2
MOS-LQO
,
4.37
3.94
3.78
3.68
64
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