A network has a plurality of edge nodes (7a, 7b, 7c, 7d) and core nodes (3a, 3b, 3c) for carrying flows of data from an ingress gateway (7a, 7b, 7c, 7d) to an egress gateway (7a, 7b, 7c, 7d) along a path of core nodes. For any given path in the network work from an ingress node to an egress node, the number of flows is controlled. When network congestion occurs, the egress gateway (7a, 7b, 7c, 7d) provides an indication of the level of network congestion. Terminating flows is disruptive and therefore the ingress gateway (7a, 7b, 7c, 7d) can mark other flows with a congestion marker and send them to the egress gateway (7a, 7b, 7c, 7d). These marked flows are routed by the core and egress gateway (7a, 7b, 7c, 7d) but ignored for calculating network congestion. When the network congestion is alleviated, the marked flows can be un-marked and treated as normal flows, hence the network avoids unnecessary flow termination.