http://www.rfc-editor.org/rfc/rfc6157.txt
RFC 6157: IPv6 Transition in the Session Initiation Protocol (SIP), G. Camarillo, K. El Malki, V. Gurbani2011-04-01T23:00:00-00:00This document describes how the IPv4 Session Initiation Protocol (SIP) user agents can communicate with IPv6 SIP user agents (and vice versa) at the signaling layer as well as exchange media once the session has been successfully set up. Both single- and dual-stack (i.e., IPv4-only and IPv4/IPv6) user agents are considered. [STANDARDS-TRACK]