Early Media

Different application servers may implement early media in different ways. In general, the SBC supports early media in the following way.

If the SBC receives an SDP without any cookie in a provisional response, the SBC generates its own SRTP crypto context and exchanges it with the caller via the SDP included in the provisional response. The SBC continues to decrypt and encrypt early media packets going to and from the caller. The SBC stops decrypting and encrypting only if it receives a final response with an answer SDP that signals that SRTP Pass-through should be enabled.