研究STUN协议
Number: RFC3489（ftp://ftp.rfc-editor.org/in-notes/rfc3489.txt）
Title: STUN - Simple Traversal of User Datagram Protocol (UDP)
Through Network Address Translators (NATs)
Author or Ed.: J. Rosenberg, J. Weinberger, C. Huitema, R.
Mahy
Date: March 2003
Format: ASCII
Status: PROPOSED STANDARD