IETF RFC 7403 PDF

SIP already provides the ability to perform hop-by-hop traceroute for SIP messages using the Max-Forwards header field to determine the reachability path of requests to a target. A mechanism for medialoopback calls has also been defined separately, which enables test calls to be generated that result in media being looped back to the originator. This document describes a means of performing hop-by-hop traceroute-style test calls using the media-loopback mechanism to test the media path when SIP sessions go through media-relaying backto- back user agents (B2BUAs).