In many SIP deployments, SIP entities exist in the SIP signaling path between the originating and final terminating endpoints,

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There is a need for having a globally unique session identifier for the same SIP session that can be consistently maintained across SIP Proxies, Back-to-Back User Agents (B2BUAs), and other SIP middleboxes, for the purpose of troubleshooting. This document proposes a new SIP header to carry such a value: Session-ID.

This document describes the behavior of signaling intermediaries in Real-Time Communication (RTC) deployments, sometimes referred to as Session Border Controllers (SBCs), when performing Hosted NAT Traversal (HNT). HNT is a set of mechanisms, such as media relaying and latching, that such intermediaries use to enable other RTC devices behind NATs to communicate with each other.This document is non-normative and is only written to explain HNT in order to provide a reference to the Internet community and an informative description to manufacturers and users.

The Session Initiation Protocol (SIP) was devel-<br />oped to control multi-media sessions on the Internet. Shortly<br />after its debut as a standard in 1999, SIP was adopted<br />by the 3rd Generation Partnership Project (3GPP) as the<br />preferred signaling protocol for the Internet Multimedia<br />Subsystem (IMS). This adoption provided a boost to the<br />nascent protocol as traditional telecommunication services<br />were interpreted in the context of the new protocol and<br />as SIP introduced richer services in the form of instant<br />messaging and rich presence to traditional telephony. In<br />this paper, we study the evolution of the protocol from its<br />roots to its use in operational networks today and the issues<br />it faces in such networks. We also provide a glimpse to the<br />continued progression of SIP in Peer-to-Peer (P2P) networks<br />and take a critical look at where SIP has succeeded, and<br />more importantly, where it has failed to meet expectations.<br /><br />