Flow-Level Precision Congestion Control for SRv6 Networks

This document defines a flow-level precision congestion control mechanism for SRv6 networks. The mechanism specifies new congestion notification message formats that enable per-flow congestion information delivery and hop-by-hop backpressure control. Compared to traditional Priority-based Flow Control (PFC) which operates at the queue level, this mechanism provides finer-grained congestion control suitable for Wide-Area Network (WAN) environments, mitigating head-of-line blocking, congestion spreading, and deadlock issues. The document also describes interoperability models with traditional IEEE 802.1Qbb PFC.