using at least one transmit-queue in a network element, transmitting packets from at least two sources to a headroom buffer in a peer network element, each source having a predefined sub-priority level different from the sub-priority levels of the other of the at least two sources, such that the transmit-queue transmits packets of a plurality of different sub-priority levels;

receiving from the peer network element signaling that indicates a number of credits for transmitting packets to the peer network element;

manage for at least one specific one of the at least one transmit-queue, a current number of credits available for transmission from the at least one specific transmit-queue, responsive to the signaling;

selecting a threshold priority based on the current number of credits for the at least one specific transmit-queue; and

for the at least specific transmit-queue, transmitting packets associated with data sources of the at least one specific transmit-queue that are higher in sub-priority level than the threshold priority, and refraining from transmitting other packets associated with the at least one specific transmit-queue.