Transcoding Mode; Prioritizing Coder List In Sdp Offer - AudioCodes Mediant 4000 SBC User Manual

a=rtpmap:96 telephone-event/8000
a=fmtp:96 0-15
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a=sendrecv
3. The device includes only the G.729 and G.726 coders in the SDP offer that it sends
from the outgoing leg to the outbound SIP entity. The G.729 is listed first as the
Allowed Audio Coders Group for coder restriction takes precedence over the
extension coder.

To configure coder transcoding:
1. In the Coder Groups table, configure a Coders Group for extension coders. For more
information, see ''Configuring Coder Groups'' on page 409.
2. In the IP Profiles table, configure the IP Profile associated with the SIP entity:
a. Assign the Coders Group to the IP Profile, using the 'Extension Coders Group'
parameter (SBCExtensionCodersGroupName).
b. Enable extension coders by configuring the 'Allowed Coders Mode' parameter to
Restriction or Restriction and Preference.
Note:
•
To implement transcoding, you must configure the number of required DSP
channels for transcoding (for example, MediaChannels = 120). Each transcoding
session uses two DSP resources.
•
The transcoding mode can be configured globally, using the TranscodingMode
parameter or for specific calls, using the IP Profiles table.

21.5.5 Transcoding Mode

By default, the device performs transcoding only if required. This refers to all types of
transcoding (interworking) that require DSPs such as voice coder transcoding, DTMF
negotiations, and fax negotiations. Transcoding is required, for example, when two SIP
entities use different coders. In such a scenario, you would need to configure transcoding
(i.e., extension coders), the device performs coder transcoding between the legs (inbound
and outbound). If the SIP entities use the same coder, the device does not perform
transcoding.
Alternatively, you can configure the device to always perform transcoding, regardless
whether it is required or not. This is referred to as forced transcoding. For example, if the
SIP entities use the same coder, the device performs transcoding of the same coder (e.g.,
G.711 and G.711) between the two legs.
The transcoding mode can be configured globally (TranscodingMode parameter) or per
SIP entity using IP Profiles (IpProfile_TranscodingMode parameter).
Note: If the transcoding mode is configured to Force (i.e., always performs
transcoding) for an IP Profile associated with a specific SIP entity, the device also
applies forced transcoding for the SIP entity communicating with this SIP entity,
regardless of its IP Profile settings.

21.5.6 Prioritizing Coder List in SDP Offer

In addition to restricting the use of coders using Allowed Audio Coders Groups (see
''Configuring Allowed Audio Coder Groups'' on page 414), you can also prioritize the coders
User's Manual 468
Mediant 4000 SBC
Document #: LTRT-40203