Schulzrinne, H., McCann, S., Bajko, G., Tschofenig, H., and D. Kroeselberg, "Extensions to the Emergency Services Architecture for Dealing With Unauthenticated and Unauthorized Devices", RFC 7406, DOI 10.17487/RFC7406, December 2014, <https://www.rfc-editor.org/info/rfc7406>.