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Global SIP Settings
41-001343-02 REV04 – 05.2014 4-77
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. The default payload setting is to allow all codecs. You can set payload to use only basic codecs (G.711 u-Law,
G.711 a-Law, G.729), and/or Adaptive Multi-Rate (AMR) and Adaptive Multi-Rate Wideband (AMR -WB) (G.722.2) codecs (for
the 6735i, 6737i, 6863i, 6865i, and 6867i IP phones if a license is available), or select from up to 14 codecs for the phones
AND customize a codec preference list of up to 10 codecs. In the Aastra Web UI, codecs 2 through 10 can be set to “None”
if required (no codecs).
Ptime (packetization time) is a measurement 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 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 deter-
mine whether each individual packet contains useful speech data. Enabling silsupp results in decreased network band-
width, by avoiding the transmission of 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 (in numerical order of payload).
Note:
In the Aastra Web UI:
• Setting Codec 1 to “All” ignores the packetization interval (ptime). The packetization interval setting defaults to 30,
which is the default for all codecs.
• Setting Codec 1 to “All” automatically sets all other codec preference fields 2 through 10 to “None”.
• Setting Codec 1 to “Basic” and all other codec preferences in 2 through 10 to “None”, forces the phone to use only the
basic codecs as in previous releases (G.711 u-law, G.711 a-law, and G.729). If you select an additional codec to use in
the codec preferences 2 through 10 fields, those codecs are added to the list of Basic codecs for the phone to use.