Transcoding Processing Overview
Transcoding processing is viewed in terms of the ingress and egress realms. The ingress realm is where the SDP offer is received by the Oracle® Enterprise Session Border Controller. The egress realm is where the SDP offer is sent, and where the SDP answer is expected to be received from (i.e., the answerer's realm). A call is defined as transcodable if an egress or ingress policy exists for the session and if the session is not subject to media release, as specified in the realm configuration.
To understand the details of transcoding processing, refer to the following diagram. An SDP offer, O0, is received by the Oracle® Enterprise Session Border Controller in the ingress realm. The ingress codec policy is applied here and the SDP offer is transformed into O1. O1 is then passed to and processed by the egress codec policy. This SDP message is then forwarded to the answerer as O2. The answerer replies with A0 to the Oracle® Enterprise Session Border Controller, which is subjected to the egress codec policy again and transformed into A1.
When policy dictates not to transcode the call, the Result SDP sent back to the offerer is based on the common codecs shared between A1 and O1. The Oracle® Enterprise Session Border Controller first constructs the list of codecs that are present in both in O1 and A1. Then, the Oracle® Enterprise Session Border Controller maintains the codec order from A1 for the Result as it is sent to the offerer.
When policy dictates to transcode the call, the top transcodable codec in O1 is used in the ingress realm and the top non-signaling codec in A1 is used in the egress realm.
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