Transcoding Mode; Prioritizing Coder List In Sdp Offer - AudioCodes Mediant 800B User Manual

Notes:
•
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 Profile table.

28.5.5 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.

28.5.6 Prioritizing Coder List in SDP Offer

In addition to restricting the use of coders using Allowed Coders Groups (see ''Configuring
Allowed Audio Coder Groups'' on page 641), you can also prioritize the coders listed in the
SDP offer. This feature is referred to as Coder Preference and applies to both SBC legs:

Incoming SDP offer: The device arranges the coder list in the incoming SDP offer
according to the order of appearance of the Allowed Coders Group that is associated
with the incoming dialog. The coders listed higher up in the group take preference
over ones listed lower down. To configure this, configure the 'Allowed Coders Mode'
parameter (IpProfile_SBCAllowedCodersMode) in the associated IP Profile to
Preference or Restriction and Preference. If you configure the parameter to to
Preference, the coders in the SDP offer that also appear in the Allowed Coders Group
are listed first in the SDP offer, and the coders in the SDP offer that do not appear in
the Allowed Coders Group are listed after the Allowed coders in the SDP offer.
Therefore, this setting does not restrict coder use to Allowed coders, but uses
(prefers) the Allowed coders whenever possible.

Outgoing SDP offer: If only Allowed coders are used, the device arranges the coders
in the SDP offer as described above. However, if Extension coders are also used, the
coder list is arranged according to the SBCPreferencesMode parameter. Depending
on the parameter's settings, the Extension coders are added after the Allowed coders
according to their order in the Allowed Coders Group, or the Allowed and Extension
coders are arranged according to their position in the Allowed Coders Group.
User's Manual
Mediant 800B Gateway and E- SBC
616 Document #: LTRT-10296