[1] RFC 3427 - Change Process for the Session Initiation Protocol (SIP) () <https://tools.ietf.org/html/rfc3427>
[2] RFC 6709 - Design Considerations for Protocol Extensions () <https://tools.ietf.org/html/rfc6709#section-3.2.1>
[3] RFC 5727 - Change Process for the Session Initiation Protocol (SIP) and the Real-time Applications and Infrastructure Area () <https://tools.ietf.org/html/rfc5727#section-4>