Ericsson AB University of Glasgow Nemu Dialogue Systems Oy Cisco Systems, Inc. This document describes a feedback message intended to enable congestion control for interactive real-time traffic. The RTP Media Congestion Avoidance Techniques (RMCAT) Working Group formed a design team to analyze feedback requirements from various congestion control algorithms and to design a generic feedback message to help ensure interoperability across those algorithms. The feedback message is designed for a sender-based congestion control, which means the receiver of the media will send necessary feedback to the sender of the media to perform the congestion control at the sender.