CoS Process on Incoming Packets

Classifiers and policers perform the following operations on incoming packets:

A classifier examines an incoming packet and assigns a forwarding class and loss priority to it.
Based on the forwarding class, the packet is assigned to an outbound transmission queue.
Input policers meter traffic to see if traffic flow exceeds its service level. Policers might discard, change the forwarding class and loss priority, or set the PLP bit of a packet. A packet for which the PLP bit is set has an increased probability of being dropped during congestion.