Multi-level Congestion Response Framework with Long-haul Congestion Notification for DCI Networks

This document specifies a multi-level congestion response framework and an associated Long-haul Congestion Notification Packet (Long-haul CNP) for Data Center Interconnect (DCI) wide-area network scenarios. The framework defines a graduated congestion response mechanism: lightweight ECN marking for incipient congestion and device- originated Long-haul CNP for severe or rapidly worsening congestion. Long-haul CNP packets carry explicit control instructions (e.g., rate reduction percentage, pause duration) and are sent directly by congestion-aware intermediate nodes to the traffic source via unicast, reducing feedback latency compared to receiver-mediated congestion notification. The document also specifies a multi-device collaborative suppression mechanism and BDP-adaptive dynamic threshold calculation for long-haul links. Two packet encapsulation formats are defined: an ICMPv6 extension and a RoCEv2 backward- compatible extension.