Transcoding Modes - AudioCodes Mediant 800B User Manual

User's Manual
Notes:

27.4.4 Transcoding Modes

The device supports the configuration of the voice transcoding mode (media negotiation)
between the two SBC legs. The device can be configured to perform transcoding only
when necessary. Typically, the SBC passes RTP packets transparently (RTP-to-RTP)
between the two user agents. If the device is configured to always perform transcoding,
then transcoding is performed on the outgoing SBC leg and the device's SBC application
interworks the media by implementing PSTN transcoding (since both legs have different
media capabilities).
In the SBC application, forced transcoding of voice in an SBC session allows the device to
receive capabilities that are not negotiated between the SBC legs. For example, if on the
SBC session you want to force Gain Control to use voice transcoding even though both
sides of the session have negotiated without SBC intervention (for example, coder
extension).
The transcoding mode can be configured using the parameters TranscodingMode and
IPProfile.
Note:
Version 6.6

No Media Anchoring can be used when the SBC does not do NAT
traversal (for media) where all the users are in the same domain.

No Media Anchoring calls cannot operate simultaneously with the
following SBC features:
- Force transcoding
- Extension Coders
- Extension of RFC 2833/Out-of-band DTMF/In-band DTMF
- Extension of SRTP/RTP
All restriction features (Allowed Coders, restrict SRTP/SRT, restrict RFC
2833) can operate simultaneously. Once No Media Anchoring is enabled,
the features listed above are disabled.

The Coder Restriction feature operates simultaneously with No Media
Anchoring calls. Restricted coders are removed from the SDP offer
message.

When two UA's pertain to the same SRD, the parameter
IntraSRDMediaAnchoring is set to 1, and one of the UA's is defined as a
foreign user (example, "follow me service") located in the WAN, while the
other UA is located in the LAN: calls between these two UA's can't be
established until IntraSRDMediaAnchoring is set to 0, as the device
doesn't interfere in the SIP signaling. In other words, parameters such as
IP addresses are not manipulated for calls between LAN and WAN
(although required).

When the parameter SBCDirectMedia is disabled, No Media Anchoring
calls between two UA's belonging to separate SRD's cannot be
configured. No Media Anchoring calls between two UA's belonging to the
same SRD is configurable only (in this case).
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.
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Mediant 800B GW & E-SBC