Restricting Coders; Coder Transcoding - AudioCodes Mediant 1000B User Manual

User's Manual

28.4.5 Restricting Coders

The SBC Allowed Coders (coders restriction) feature determines the coders that can be
used for a specific SBC leg. This provides greater control over bandwidth by enforcing the
use of specific coders (allowed coders groups) while preventing the use of other coders.
This is done by defining a group of allowed coders for the SBC leg, as described below:
1. Configure a Coders Group for allowed coders, using the AllowedCodersGroup
parameter.
2. Select this Coders Group using the SBCAllowedCodersGroupID parameter of the IP
Profile table.
3. Enable this feature by setting the SBCAllowedCodersMode parameter of the IP Profile
table to Restriction.
Coders that are not listed (including unknown coders) in the Allowed Coders Group are
removed from the SDP offer. Therefore, only coders common between the SDP offer and
Allowed Coders Group are used. If the SDP offer does not list any of the Allowed Coders,
the call is rejected, unless transcoding is configured using Extension coders (see Coder
Transcoding on page 495).
Notes:
•
For a list of supported coders, see ''Configuring Default Coders'' on page 295.
•
Allowed Coder Groups are applicable only to audio media.
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: G.729, G.711, and G.723.

The source (first) leg includes the following Allowed Coders: G.711 and G.729.
The device selects the common coders, i.e., G.711 and G.729 (with changed preferred
coder priority - highest for G.711). 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.

28.4.6 Coder Transcoding

The device can add coders, referred to as Extension coders to the SDP offer in the
outgoing leg.
For example, assume the following:

The SDP coder offer includes the following coders: G.729, G.711, and G.723.

The incoming leg includes the following Allowed coders: G.711 and G.729.
1. The device selects the common coders, i.e., G.711 and G.729 (with changed
preferred coder priority - highest for G.711). 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.
2. Assuming that the outgoing leg also includes Allowed coders and/or Extension coders:
The device performs the Allowed coders procedure (common coders) between the
Version 6.8 495 Mediant 1000B Gateway & SBC
28. SBC Overview