H3C MSR 20-20 Command Reference Manual page 2563

Msr 20/30/50 series routers

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Table 672 G.729 algorithm

G.729 algorithm: media stream bandwidth 8 kbps, minimum packet assembly interval 10 ms.

Packet assembly interval is the duration to encapsulate information into a voice

Bytes coded in a time unit = packet assembly interval X media stream

Packet length (IP) = IP header + RTP header + UDP header + voice information

length = 20+12+8+data

Packet length (IP+PPP) = PPP header + IP header + RTP header + UDP header +

voice information length = 6+20+12+8+data

Network bandwidth = Bandwidth of the media stream X packet length / bytes

coded in a time unit

Since IPHC compression is affected significantly by network stability, it cannot

achieve high efficiency unless line is of high quality, network is very stable, and

packet loss does not occur or seldom occurs. When the network is unstable, IPHC

efficiency drops drastically. With best IPHC performance, IP (RTP) header can be

compressed to 2 bytes. If PPP header is compressed at the same time, a great deal

of media stream bandwidth can be saved. The following table shows the best

IPHC compression efficiency of codec algorithms with packet assembly interval of

Table 673 Compression efficiency of IPHC+PPP header

Two communication parties can communicate normally only if they share some

identical coding/decoding algorithms. If the codec algorithm between two

connected devices is not consistent, or the two devices share no common

coding/decoding algorithms, the calling will fail.

Before compression

After IPHC+PPP compression

Packet length

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