📝SDP Offer/Answer model
Is the model of using SDP defined in RFC 3264.
Two roles are: Offerer and Answerer.
Offerer sends an SDP offer (what it want to receive)
Answerer replies with SDP Answer (what it will send)
To reject a media stream, answerer sets its port to 0.
SDP Offer/Answer model is used by SIP and WebRTC.