Malis, A., Brayley, J., Shirron, J., Martini, L., and S. Vogelsang, "Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) Circuit Emulation Service over MPLS (CEM) Encapsulation", RFC 5143, DOI 10.17487/RFC5143, February 2008, <https://www.rfc-editor.org/info/rfc5143>.