Pre-congestion notification (PCN) is a mechanism designed to protect the quality of service of inelastic flows. It does this by marking packets when traffic load on a link is approaching or has exceeded a threshold below the physical link rate. This document specifies an extension to the two-state PCN baseline encoding that enables three encoding states to be carried in the IP header without using more than one Diffserv codepoint. It presupposes a standards action has removed the limit of two encoding states in current tunnelling mechanisms.