Avaya 555-245-600 사용자 설명서

For each codec, there was an attempt to verify that the audio packets were received intact. This 
was done by spot checking the audio packets before and after compression, using two Sniffer 
protocol analyzers. For every codec except G.711, the RTP header and payload were identical 
before and after compression. With G.711, however, the received packets had the PADDING 
flag set in the RTP header, although the flag was not set when the packets were transmitted. 
The PADDING flag indicates the presence of padding octets at the end of the RTP payload, 
which cannot be true for G.711.

To configure RTP header compression on a Cisco router:

1. Specify the number of RTP connections that can be compressed (cache allocation). In 

interface configuration mode, the command is ip rtp compression-connections 
<number>

, where

●

The default for <number> is 32, and each call requires two connections.

●

The configurable range is 3 to 256 for PPP and HDLC using IOS v11.3 and later.

●

The configurable range is 3 to 1000 for PPP and HDLC using IOS v12.0(7)T and later.

●

For Frame Relay, the value is fixed at 256.

2. The command to turn on compression is ip rtp header-compression in interface 

configuration mode. It must be implemented at both ends of the WAN link. When the 
command was entered into the router, ip tcp header-compression was also installed 
automatically. When either command was removed, the other was automatically removed.

G.711 

(64 kbps)

160

50

84

68.5

~18%

G.729A 

(8 kbps)

20

50

27.5

13

~53%

G.723.1 

(5.3 kbps)

20

33

18

9

~50%

G.723.1 

(6.3 kbps)

24

33

19

10

~47%