NAT/Firewall traversal for SIP: issues and solutions

Traversal of the session initiation protocol (SIP) and the sessions it establishes through network address translators (NATs) is a challenge for IP communications. The status of near-ubiquitous deployment of NAT across the Internet and the great diversity of their behavior raise a serious obstacle in the SIP's deployment. This paper analyzes different SIP deployment scenarios and traversal mechanisms for media traffic and recommends several methods for NAT traversal.