Transcoding Modes - AudioCodes Mediant 1000B User Manual

handled as No Media Anchoring (direct media) calls. This occurs even if the global
parameter is disabled.
Notes:
•
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 with the following features:
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√
√
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√
•
All restriction features (Allowed Coders, restrict SRTP/RTP, restrict RFC 2833)
can operate with No Media Anchoring calls. Restricted coders are removed from
the SDP offer message.
•
For No Media Anchoring, opening of voice channels and allocation of IP media
ports are not required.
•
When two UAs belong to the same SRD which is enabled for No Media Anchoring,
and one of the UAs 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 UAs cannot be established until the No Media Anchoring for the SRD is
disabled, as the device does not 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 global parameter SBCDirectMedia is disabled, No Media Anchoring can
only occur for calls between UAs belonging to the same SRD that is configured for
No Media Anchoring in the SRD table.

28.4.4 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 globally, using the TranscodingMode parameter
or for specific calls, using the IP Profile table.
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.
•
It is recommended to use the MPM(s) when transcoding is required.
User's Manual
Manipulation of SDP data (offer/answer transaction) such as ports, IP
address, coders
Force transcoding
Extension Coders
Extension of RFC 2833 / out-of-band DTMF / in-band DTMF
Extension of SRTP/RTP
Mediant 1000B Gateway & SBC
494 Document #: LTRT-27034