This document defines an alternative connection model for Message Session Relay Protocol (MSRP) User Agents (UAs); this model uses the connection-oriented media (COMEDIA) mechanism in order to create the MSRP transport connection. The model allows MSRP UAs behind Network Address Translators (NATs) to negotiate which endpoint initiates the establishment of the Transmission Control Protocol (TCP) connection, in order for MSRP messages to traverse the NAT. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the

NAT Traversal Practices for Client-Server SIP 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. Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Not all documents approved by the IESG are a candidate for any level of Internet Standard; see Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at