In WebRTC (P2P Mesh), why is a STUN server required?

1. A To allow a client to discover its true public-facing IP address and port mapping; since internal 192.168.x.x addresses are not globally reachable, peers must know this public identity to connect.
2. B To act as a high-bandwidth relay that proactively tunnels and re-transmits the entire encrypted video stream between two physical peers that are unable to establish a direct connection.
3. C To implement a mandatory system-level encryption layer that prevents any intermediate internet service provider from performing deep-packet inspection on the P2P traffic.
4. D To maintain a synchronized global database of all active call participants, ensuring that the mesh network can be properly reconstructed if a single user suddenly disconnects.