Drop congestion notification (DCN)

Supported devices can function as transit switches for drop congestion notification (DCN). DCN is a congestion management technique based on packet trimming. Rather than dropping a packet when congestion occurs, the packet?s payload is trimmed, resulting in a smaller packet that is then transmitted through a high-priority queue toward its destination. Subsequent hops in the network recognize DCN-marked packets and direct them to high-priority queues. End hosts must process the trimmed DCN packets, identify the packets dropped due to congestion, and request retransmission of those lost packets. The original sender host, upon receiving the DCN feedback, immediately re-transmits the dropped packet and adjusts the flow rate. 

DCN works only for UDP unicast traffic. To enable DCN on the switch, set the UDP port number (udp-port port-number) and a strict-high priority forwarding class (forwarding-class class-name) at the [edit class-of-service drop-congestion-notification] hierarchy. The L4 UDP port number is set to the DCN protocol number so that the switch can identify the DCN packets.

Then set drop-congestion-notification on an ingress interface at the [edit class-of-service interface ingress-interface-name] hierarchy level so that the interface can detect the DCN-marked packets.