Ericsson Skype Skype NS-Technologies Traversal of the Session Initiation Protocol (SIP) and the sessions it establishes through Network Address Translators (NATs) is a complex problem. Currently, there are many deployment scenarios and traversal mechanisms for media traffic. This document provides concrete recommendations and a unified method for NAT traversal as well as documents corresponding flows. This document is not an Internet Standards Track specification; it is published for informational purposes.