A source node receives related frames of data to be transmitted from the source node to a destination node and places the frames in a queue. The queue is associated with a communication path over which the related frames are to be transmitted to the destination node. An interface that couples the source node to the communication path receives an indication directed to the source node of traffic congestion in the communication path. In response, the source node controls the rate at which the related frames of data are transferred from the queue to a transmit buffer accessible to the interface, in order to relieve the traffic congestion in the communication path.