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• accepting the SDP answer received in 18x on same dialog as active dialog (to support media redirection case),
• accepting the SDP answer received in 18x response on different dialog than the active dialog (forking case),
• or not sending modified SDP answer in 18x response, and instead sending the new offer towards the caller using SIP UPDATE (early dialog).

SBC is enhanced to support transcoding active early media from subsequent 18x responses from different dialogs if the ingress peer does not support 100rel to ensure the ingress peer receives what is expected as per SDP negotiations.

• If the SBC is configured for "Downstream Forking" and to accept the Last Provisional Response (default value), and multiple 18xs from different sources are received on egress peer, the SBC does not change the early media on ingress leg. For any subsequent changes in an active early media on egress peer, SBC makes the call as either pass-through or transcoded accordingly without changing the codec on the ingress early dialog.
• If the codec received in a subsequent 18X response from the egress peer is the same as what was sent in the first 18X response on the ingress side, then SBC makes the call as a pass-through call.
• If the codec received in a subsequent 18X response from egress peer is different from what was sent in the first 18X response on the ingress side, the SBC forces the call to transcode even though pass-through is possible.
• Once a call becomes stable, the SBC initiates a Re-INVITE on the ingress peer, as needed, for updating any additional SDP changes.
• If the ingress endpoint does not support 100rel, the SBC retains the same codec on the ingress endpoint without any change when "Dialog ID Transparency" configuration is enabled.
• If the ingress endpoint supports 100rel, there is no change to existing SBC functionality when "Dialog ID Transparency" feature is enabled.
• The SBC continues to stay in the call when it is unable to do transcoding for an early dialog and it retains the same early media that was currently active.
• The SBC gracefully terminates the call if a final answer is received on an early dialog for which transcoding is not supported.
• The SBC does not trigger this feature if SBC is configured for "Down Stream Forking" and to accept the First Provisional Response.