3.1.5.12 Early Media Support

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Early media refers to media exchange taking place before a session INVITE is accepted. This could be the initial greeting received by the user while the SIP handshake is under way. Early media support amounts to getting an SDP answer in a provisional SIP response of the 18x levels and starting media exchange after processing the SDP answer. Provisional responses are specified in detail in [RFC3261] section 13. Early media support discussed in this document is not based on any specific standards protocol. It is the subject of the following sections.