Media Anchoring Without Transcoding (Transparent) - AudioCodes Mediant 8000 Installation, Operation & Maintenance Manual

Installation & Operation Manual
According to the above functionalities, the call can be configured to operate in one of
the following modes:
Media Anchoring without Transcoding (Transparent): RTP traverses the

device with minimal RTP packet changes (no DSP resources required). This is
typically used to solve NAT, firewall, and security issues. In this mode, all the
"audio" coders in the received offer are included in the SBC application outgoing
offer. The Coder Table configuration has no effect on the coders in the outgoing
offer.
Media Anchoring with Transcoding: RTP traverses the device and each leg

uses a different coder or coder parameters (DSP resources are required).
43.16.1

Media Anchoring without Transcoding (Transparent)

To direct the RTP to flow through the device (for NAT traversal, firewall and security),
all IP address fields in the SDP are modified:

Origin: IP address, session and version id

Session connection attribute ('c=' field)

Media connection attribute ('c=' field)

Media port number

RTCP media attribute IP address and port (if the parameter Enable RTCP
Attribute is set to 1)
Each SBC leg allocates and uses the device's local ports (e.g., for RTP\RTCP\fax).
The local ports are allocated from a Media Realm associated with each SBC leg. SBC
legs are associated with a Media Realm as follows: If the leg's IP Group is configured
with a Media Realm, then this is the associated Media Realm; otherwise, the leg's
SRD Media Realm is the associated one.
Figure 43-9: Example of a SIP call with Media Anchoring without Transcoding
Version 6.6
43. Session Border Controller (SBC) Application
771 October 2014