Adaptive flow prioritization

A method for communication, comprising:

• receiving from a packet data network, via ingress interfaces of a switching element, packets belonging to multiple flows, and forwarding the packets to respective egress interfaces of the switching element for transmission to the network;
• for each egress interface of the switching element, queuing the packets, belonging to a plurality of the flows, that have been forwarded for transmission through the egress interface;
• and
• for each of one or more of the egress interfaces, in each of a succession of arbitration cycles:
• assessing a respective number of the packets in each of the plurality of the flows that are queued for transmission through the egress interface;
• assigning the flows for which the respective number is zero to a first group, while assigning the flows for which the respective number is non-zero to a second group;
• and
• after assigning the flows, transmitting to the network the received packets that have been forwarded to the egress interface and belong to the flows in the first group with a higher priority than the flows in the second group.