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End-to-end QoS
Figure 477 End-to-end QoS model
As shown in Figure 477, traffic classification and congestion management provide the foundation for a
network to provide differentiated services:
• Traffic classification—Uses specific match criteria to organize packets with different characteristics
into different classes. Traffic classification is typically applied to the inbound direction of a port.
• Congestion management—Provides a resource scheduling policy to arrange the forwarding
sequence of packets when congestion occurs. Congestion management is typically applied to the
outbound direction of a port.
Traffic classification
When defining match criteria for classifying traffic, you can use IP precedence bits in the type of service
(ToS) field of the IP packet header. You can also use header information such as IP addresses, MAC
addresses, IP protocol field, and port numbers. You can define a class for packets with the same
quintuple (source address, source port number, protocol number, destination address and destination
port number for example), or for all packets to a network segment.
When packets are classified on the network boundary, the precedence bits in the ToS field of the IP
packet header are typically reset. In this way, IP precedence can be directly used to classify the packets
in the network. IP precedence can also be used in queuing to prioritize traffic. The downstream network
can either use the classification results from its upstream network or reclassify the packets according to its
own criteria.
To provide differentiated services, traffic classes must be associated with specific traffic control actions or
resource allocation actions.
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