SIP User's Manual 500 Document #: LTRT-12804
Mediant 800 MSBG
This feature also allows the definition of a coders preference policy for the SDP offered
coders. Coders Preference is done on both legs on the original SDP offer (without the
extended coders), and the offered side selects its chosen coders from the suggested
coders list. Coders listed higher up in the Allowed Coders Group take preference over ones
listed lower down in the group.
To configure whether you want to enable only the Allowed Coders list feature, only the
Allowed Coders Preference feature, or both, use the IP Profile parameter,
SBCAllowedCodersMode.
Notes:
• For a list of supported coders, refer to the ini file parameter table
CodersGroup.
• If Allowed Coder Groups are configured, unknown coders are blocked by
the device.
• Allowed Coder Groups are applicable only to audio media.
• Allowed Coder Groups can be assigned to IP Profiles (using the IPProfile
parameter).
• For configuring Allowed Coder Groups (and Extension Coder Groups),
use the parameter AllowedCodersGroup.
The Allowed Coders process is as follows:
a. The device receives an incoming SIP message with SDP (offer) and checks the
offered coders.
b. The source (first) leg may have Allowed Coders (i.e. list of coders that can be used -
enforced).
c. The device checks for common coders between the SDP offered coders and the
Allowed Coders Group list.
For example, assume the following:
The SDP coder offer includes the following coders: G729, G711, and G723.
The source (first) leg includes the following Allowed Coders: G711 and G729.
The device selects the common coders, i.e., G711 and G729 (with changed preferred
coder priority - highest for G711). In other words, it removes the coders that are not in the
Allowed Coders list and the order of priority is first according to the Allowed Coders list.
Now assume that the destination (second) leg also includes Allowed Coders and/or
extensions. Therefore, the device performs the Allowed Coders procedure (common
coders) between the updated coder list and the destination leg's Allowed Coders list
(Coders Extension procedure is performed before Allowed Coders). Adding to the example,
assume the following:
For the first leg, the device selects the common coders G711 and G729 (explained in
the example above).
Assume that the second leg includes the Extended coder G726.
Assume that the second leg includes the following Allowed Coders: G723, G726, and
G729.
As a result, the device selects the common coders, i.e., G729 and G726 (coder priority did
not change Extended coder order).
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