Question: In an RTSP SETUP method for establishing STKM sessions, what is the specific purpose of the 'client_port' RTP parameter in the transport request header?
Option 1: To specify the multicast UDP port for receiving broadcast content
Option 2: To indicate the server's chosen port for sending unicast STKM data
Option 3: To provide the client's chosen unicast UDP port(s) for receiving STKM data
Option 4: To negotiate the TCP protocol for STKM session establishment
Explanation: The 'client_port' parameter is used to inform the server about the unicast UDP port(s) that the client has selected to receive STKM (Secure Transmission Key Material) data, ensuring the server sends STKM data to the correct client port for successful session establishment and key material exchange.