Hautakorpi, J., Ed., Camarillo, G., Penfield, R., Hawrylyshen, A., and M. Bhatia, "Requirements from Session Initiation Protocol (SIP) Session Border Control (SBC) Deployments", RFC 5853, DOI 10.17487/RFC5853, April 2010, <https://www.rfc-editor.org/info/rfc5853>.