1-2
and jitter. As for mission-critical applications, such as transactions and Telnet, they may not require high
bandwidth but do require low delay and preferential service during congestion.
The emerging applications demand higher service performance of IP networks. Better network services
during packets forwarding are required, such as providing dedicated bandwidth, reducing packet loss
ratio, managing and avoiding congestion, regulating network traffic, and setting the precedence of
packets. To meet these requirements, networks must provide more improved services.
Major Traffic Control Technologies
Figure 1-1 End-to-end QoS model
As shown in
Figure 1-1, traffic classification, traffic policing, traffic shaping, congestion management,
and congestion avoidance form the foundation for differentiated service provisioning. They deal with
different issues of QoS:
z Traffic classification identifies traffic based on certain match criteria. It is the foundation for
providing differentiated services and is usually applied in the inbound direction of a port.
z Traffic policing confines traffic to a specific specification and is usually applied in the inbound
direction of a port. You can configure restriction or penalty measures against the exceeding traffic
to protect carrier benefits and network resources.
z Traffic shaping adapts output traffic rate, usually to the input capability of the receiving device, to
avoid packet drop and port congestion. Traffic shaping is usually applied in the outbound direction
of a port.
z Congestion management handles resource competition during network congestion. Generally, it
assigns packets to queues first, and then forwards the packets by using a scheduling algorithm.
Congestion management is usually applied in the outbound direction of a port.
z Congestion avoidance monitors the use of network resources and drops packets actively when
congestion reaches a certain degree. It relieves network load by adjusting traffic size. Congestion
avoidance is usually applied in the outbound direction of a port.
Among these QoS technologies, traffic classification is the foundation for providing differentiated
services by classifying packets with certain match criteria. Traffic policing, traffic shaping, congestion
management, and congestion avoidance manage network traffic and resources in different ways to
realize differentiated services.
QoS Features Supported by the Switch 4200G series
The Switch 4200G series support the QoS features listed in Table 1-1:
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