A multi-mode congestion control is employed in a transport network interconnecting a radio access node and a control node of a communication network. The transport network employs a window-based state providing a window-based congestion control mode for a data flow. This mode involves notifying an application level transport protocol implemented in a sending source of the communication network of any detected congestion event. If a congestion event in the transport network is detected a switch to a rate-based state is performed. The rate-based state provides a rate-based congestion control mode involving transmitting a rate-reducing message from the radio access node to the control node to trigger a reduction in the bitrate of the data flow in response to the detected congestion event.