Avaya 555-245-600 manual Configuration

RTP

Table 57: Test call (20ms-packets) results

Codec	Payload	Packets	Avg WAN BW		%
	bytes	per	consumption (kbps)		reduction
	per packet	second
			without	with
			compressi	compressi
			on	on
G.711	160	50	84	68.5	~18%
(64 kbps)
G.729A	20	50	27.5	13	~53%
(8 kbps)
G.723.1	20	33	18	9	~50%
(5.3 kbps)
G.723.1	24	33	19	10	~47%
(6.3 kbps)

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.

Configuration

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-compressionin 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.

Issue 6 January 2008 331