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Advanced Network Settings
4-58 41-001160-00, Rev 01 Release 2.0
IP Phone Administrator Guide
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
You can specify a customized Codec preference list on a global-basis using the
configuration files or the Aastra Web UI.
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