Aastra Telecom C53I Customized Codec Preference List, Customized Codec Settings, Attribute Value

IP Phone Administrator Guide Advanced Network Settings

Configuring the IP Phones

Customized Codec Preference List

You can also configure the IP phones to use preferred Codecs. To do this, you must enter the payload value (payload), the packetization time in milliseconds (ptime), and enable or disable silence suppression (silsupp).

Payload is the codec type to be used. This represents the data format carried within the RTP packets to the end user at the destination. You can enter payload values for G.711 a-law, G.711 u-law, and G.729a.

Ptime (packetization time) is a measurment of the duration of PCM data within each RTP packet sent to the destination, and hence defines how much network bandwidth is used for transfer of the the RTP stream. You enter the ptime values for the customized Codec list in milliseconds. (See table below).

Silsupp is used to enable or disable silence suppression. Voice Activity Detection (VAD) on the IP phones is used to determine whether each individual packet contains useful speech data. Enabling silsupp results in decreased network bandwidth, by avoiding sending RTP packets for any frame where no voice energy was detected by the VAD.

You must enter the values for this feature in list form as shown in the following example:

payload=8;ptime=10;silsupp=on; payload=0;ptime=10;silsupp=off

The valid values for creating a Codec preference list are as follows.

Customized Codec Settings

Attribute	Value
payload	0 for G.711 u-Law
	8 for G.711 a-Law
	18 for G.729a
ptime (in milliseconds)	5, 10, 15, 20.......90
silsupp	on
	off

You can specify a customized Codec preference list on a global-basis using the configuration files or the Aastra Web UI.

4-58 41-001160-00, Rev 01 Release 2.0