The Media Antitrombone feature employs the “C” line trigger to use a signaling loop to pass media directly between two endpoints. This technique supports bandwidth optimization since the SBC Core is not required to handle media once the signaling loop is identified. This feature also supports SIP signaling in all the transports: UDP, TCP, TLS, IPSec, IPv4, and IPv6.

RTP Pass-through or Transcoding Using Media Loop

The Media Antitrombone feature mainly applies to IP PBX scenarios, and is useful in situations where X-DMI cannot be passed through the SIP server.

Media Antitrombone is similar to Direct Media method, but eliminates the dependency on X-DMI header to identify the direct media. Media Antitrombone instead uses SDP “C” line for the identification of the signaling loop. The following diagrams show a typical RTP pass-through (or transcoding) using media loop application, and then the same call flow using Media Antitrombone feature.

Media Antitrombone Methodology

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