A method of performing congestion notification for a data transmission (10) from a sender (14) to a receiver (11) is described. Furthermore, nodes for such a transmission as well as methods of controlling such nodes are described. The data transmission involves a first node (12) and a second node (13) between said sender and receiver. The data packets pass from said second node to said first node towards said receiver. The method comprises: —sending (S82) a message (15) from said first node to said second node, said message relating to a decision on whether to notify said receiver of a congestion condition in said data transmission, —sending (S83) an explicit congestion notification (16) from said second node to said receiver if it is decided to notify said receiver of said congestion condition.