H3C Technologies H3C SR8800 - Manual (Page 38)

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Configuring a QoS policy
QoS policy overview
A QoS policy involves three components: class, traffic behavior, and policy. You can associate a class
with a traffic behavior using a QoS policy.
Class
Classes identify traffic.
A class is identified by a class name and contains some match criteria.
You can define a set of match criteria to classify packets, and the relationship between criteria can be
one of the following:
• and—The router considers that a packet belongs to a class only when the packet matches all the
criteria in the class.
• or—The router considers that a packet belongs to a class as long as the packet matches one of the
criteria in the class.
Traffic behavior
A traffic behavior, identified by a name, defines a set of QoS actions for packets.
Policy
A policy associates a class with a traffic behavior.
You can configure multiple class-to-traffic behavior associations in a policy.
Traffic classification overview
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, or other 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 certain network segment.
When packets are classified on the network boundary, the precedence bits in the ToS field of the IP
packet header are usually 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 classify the packets again according to
its own criteria.
To provide differentiated services, traffic classes must be associated with certain traffic control actions or
resource allocation actions. What traffic control actions to use depends on the current phase and the
resources of the network. For example, CAR polices packets when they enter the network, GTS is
performed on packets when they leave the node, queue scheduling is performed when congestion
happens, and congestion avoidance measures are taken when the congestion deteriorates.