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What is Pre-Congestion Notification? Scalable, resilient admission control using packet marking techniques Two parts – Admission (for “normal” situations) and flow Pre-emption (for unusual situations, e.g. failures) Core nodes measure current load of admission-controlled traffic selectively mark packets if congestion appears imminent (hence pre-congestion) Edge nodes monitor marking between PCN ingress-egress pairs may not admit new flows, or drop (pre-empt) existing ones based on marking of packets |