A system for controlling congestion is disclosed, the system comprising a host computer (108C) adapted to run concurrent processes (402, 412) and a gateway (100C) through which communications traffic from the concurrent processes (402, 412) to corresponding concurrent processes is directed. The gateway comprises means (906) for determining available bandwidth on connections (106) between the gateway and the corresponding concurrent processes, means (910) for determining host rate control information dependent upon said available bandwidth, and means (906) for communicating the host rate control information to the host computer (108C). The host computer (108C) comprises means (406, 416) for independently controlling traffic from each said concurrent process (402, 412) to the corresponding concurrent process according to the host rate control information.