Huawei Technologies University of Twente University of Tuebingen Huawei Technologies Pre-Congestion Notification (PCN) is a means for protecting the quality of service for inelastic traffic admitted to a Diffserv domain. The overall PCN architecture is described in RFC 5559. This memo is one of a series describing possible boundary-node behaviors for a PCN-domain. The behavior described here is that for a form of measurement-based load control using three PCN marking states: not- marked, threshold-marked, and excess-traffic-marked. This behavior is known informally as the Controlled Load (CL) PCN-boundary-node behavior. This document defines an Experimental Protocol for the Internet community.