STUN is documented in RFC 5389 and may be used by clients located behind NATs to resolve their port mapping.
For example, RTSP client must provide port range to RTSP server so the later will know where to send data.
Running STUN server at the same host as RTSP server is important, as port mapping may differ for different hosts.
The above sample uses STUN Server and STUN Client components, which implements the STUN protocol. In addition, STUN client may use DSN lookup to find the server.
Binary and sources of this sample are included in the Demo version.