Systems and techniques for prioritizing network traffic based on a flow deadline are presented. Data bandwidth in a network is detected. In response to congestion in the network, a transmission control protocol (TCP) window size is reduced. The TCP window size is reduced based on time remaining until the flow deadline. In one example, the TCP window size if further reduced based on a degree of congestion in the network. In response to no congestion in the network, the TCP window size is increased by a predetermined amount.