Mammoliti, V., Pignataro, C., Arberg, P., Gibbons, J., and P. Howard, "Layer 2 Tunneling Protocol (L2TP) Access Line Information Attribute Value Pair (AVP) Extensions", RFC 5515, DOI 10.17487/RFC5515, May 2009, <https://www.rfc-editor.org/info/rfc5515>.