RFC 7350: Datagram Transport Layer Security (DTLS) as Transport for Session Traversal Utilities for NAT (STUN)
RFC 5389: Session Traversal Utilities for NAT (STUN)
RFC 5928: Traversal Using Relays around NAT (TURN) Resolution Mechanism
Datagram Transport Layer Security (DTLS) as Transport for Session Traversal Utilities for NAT (STUN)