Fast Latency and Congestion Notification

This document describes a standard-based method for fast latency and congestion notification. By combining in-network telemetry and source routing, it enables a source node to acquire a path's latency and congestion status in less than half baseline RTT. The more timely and accurate telemetry data allow the source node to apply more effective traffic steering and congestion control actions. The method is applicable to both WAN and DCN, and can be realized through existing IETF standards.