STUN stands for Simple Traversal of User Datagram Protocol (UDP) through Network Address Translators (NAT’s). It is used in several different network implementations and scenarios, one of which is VoIP. Because of the way protocols used in a SIP based VoIP call work, making calls between two SIP entities running behind NAT devices such as a router or firewall, users typically encounter problems. Examples are one way audio during a phone call or phone registration failures when trying to register to a VoIP provider or a IP PBX not residing on the same network. STUN is a protocol that helps in resolving problems. Read the full article here.