Media Anchoring Without Transcoding (Transparent) - AudioCodes Mediant 800B User Manual

User's Manual

Media Anchoring with Transcoding: RTP traverses the device and each leg uses a
different coder or coder parameters (DSP resources are required). For more
information, see ''Media Anchoring with Transcoding'' on page 530.

No Media Anchoring: The RTP packet flow does not traverse the device. Instead, the
two SIP UA's establish a direct RTP/SRTP flow between one another (see ''No Media
Anchoring'' on page 531).

28.4.1 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
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 leg. The 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. The figure below illustrates an example of SDP handling for a call
between a LAN IP Phone 10.2.2.6 and a remote IP Phone 212.179.1.13 on the WAN.
Version 6.8
Figure 28-3: SDP Offer/Answer Example
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28. SBC Overview
Mediant 800B Gateway and E-SBC