Proactive Flow Control Point Detection in WAN

[I-D.ietf-rtgwg-net-notif-ps] establishes usecases and requirements for fast notification delivery for network events (e.g., failure, congestion or state change) in modern network applications. This document proposes a proactive detection mechanism that enables the flow control notification message generating downstream node to be aware of the nearest upstream node capable of processing the message . The mechanism operates in the data plane, uses probe packets that follow the same path as data traffic, and maintains state only where needed. While proposed for flow control, the same mechanism may support other fast notification use cases that require distributed recipient node discovery.