How does the Differentiated Service model works?
Traffic entering the network is first classified and then passed through some form of admission filter.
Admission policy conditions or shape the traffic to meet the policy requirements associated with the classification.
Conditioned traffic stream is then assigned to a particular behaviour aggregate (BA) by marking the IP header DS field of the component packets with the appropriate DSCP value.
Marked IP packets receive a particular forwarding treatment, or per-hop behaviour (PHB), at each network node. This provides the differentiated services for different type of traffic.
Each node in the network uses the QoS specification to classify, mark, shape, and police traffic, and to perform intelligent queuing.