Transcoding Modes - AudioCodes Mediant 800B MSBR User Manual


Reduces CPU usage (no media handling)

Avoids interference in SDP negotiation and header manipulation on RTP/SRTP
The device handles the No Media Anchoring process as follows:
1. Identifies a No Media Anchoring call according to configuration and the call's
properties (such as source, destination, IP Group, and SRD).
2. Handles the identified No Media Anchoring call.
The No Media Anchoring feature is enabled for all calls (regardless of SRD), using the
global parameter, SBCDirectMedia. You can also enable No Media Anchoring per SRD (in
the SRD table), whereby calls belonging to this same SRD (source and destination) are
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:
√
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
•
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.

32.4.4 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 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
User's Manual 512
Mediant 800B MSBR
Document #: LTRT-12813