Question: how qos works on cisco router?
Answer: Step 1: Define the traffic. You must tell the router which traffic you want to give QoS, which you can accomplish either using an access control list (ACL) or using Network Based Application Recognition (NBAR). ... 
Step 2: Create a class-map. ... 
Step 3: Create a policy-map. ... 
Step 4: Apply the policy-map to the interface.