Abstract—Network Utility Maximization (NUM) is a well accepted theoretical concept that describes how congestion controls could cooperate to achieve an ideal sending rate allocation, for given utility functions of senders and constraints of the network. These network constraints are expressed as a “cost” in the framework. In practice, most congestion control mechanisms obtain feedback that is different from a “cost”. This paper focuses on Explicit Congestion Notification (ECN), which has been shown to be quite advantageous when it is available, e.g. with the popular Datacenter TCP (DCTCP) mechanism. However, different from a cost, ECN marks are not additive. We present a practical solution to this problem. Our solution changes how end hosts interpret the ECN signal, while the router side can be implemented via an unusual configuration of RED parameters.