18 Coders and Profiles
This section describes configuration of the coders and SIP profiles parameters.
18.1 Configuring Coders
The Coders page allows you to configure up to 10 voice coders for the device. Each coder
can be configured with packetization time (ptime), bit rate, payload type, and silence
suppression. The first coder configured in the table has the highest priority and is used by
the device whenever possible. If the remote side cannot use the first coder, the device
attempts to use the next coder in the table, and so on.
Notes:
• A specific coder can only be configured once in the table.
• If packetization time and/or rate are not specified, the default value is
applied.
• Only the packetization time of the first coder in the coder list is declared
in INVITE/200 OK SDP, even if multiple coders are defined.
• The device always uses the packetization time requested by the remote
side for sending RTP packets. If not specified, the packetization time is
assigned the default value.
• The value of several fields is hard-coded according to common standards
(e.g., payload type of G.711 U-law is always 0). Other values can be set
dynamically. If no value is specified for a dynamic field, a default value is
assigned. If a value is specified for a hard-coded field, the value is
ignored.
• If silence suppression is not configured for a coder, the settings of the
EnableSilenceCompression parameter is used.
• The G.722 coder provides Packet Loss Concealment (PLC) capabilities,
ensuring higher voice quality.
• For G.729, it's also possible to select silence suppression without
adaptations.
• If G.729 is selected and silence suppression is disabled, the device
includes 'annexb=no' in the SDP of the relevant SIP messages. If silence
suppression is enabled or set to 'Enable w/o Adaptations', 'annexb=yes'
is included. An exception to this logic is when the remote gateway is a
Cisco device (IsCiscoSCEMode).
• For defining groups of coders, which can be assigned to Tel and IP
Profiles, see 'Configuring Coder Groups' on page 193.
• For information on V.152 and implementation of T.38 and VBD coders,
see 'Supporting V.152 Implementation' on page 153.
• The Coders table can also be configured using the table ini file
parameter, CodersGroup.
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