1-3
Countermeasures
A simple solution for congestion is to increase network bandwidth, however, it cannot solve all the
problems that cause congestion because you cannot increase network bandwidth infinitely.
A more effective solution is to provide differentiated services for different applications through traffic
control and resource allocation. In this way, resources can be used more properly. During resources
allocation and traffic control, the direct or indirect factors that might cause network congestion should be
controlled to reduce the probability of congestion. Once congestion occurs, resource allocation should
be performed according to the characteristics and demands of applications to minimize the effects of
congestion.
QoS Technology Implementations
End-to-End QoS
Figure 1-2
End-to-end QoS model
As shown in
Figure 1-2
, traffic classification, traffic policing, traffic shaping, congestion management,
and congestion avoidance are the foundations for a network to provide differentiated services. Mainly
they implement the following functions:
z
Traffic classification uses certain match criteria to organize packets with different characteristics
into different classes. Traffic classification is usually applied in the inbound direction of a port.
z
Traffic policing polices particular flows entering or leaving a device according to configured
specifications and can be applied in both inbound and outbound directions of a port. When a flow
exceeds the specification, some restriction or punishment measures can be taken to prevent
overconsumption of network resources.
z
Traffic shaping proactively adjusts the output rate of traffic to adapt traffic to the network resources
of the downstream device and avoid unnecessary packet drop and congestion. Traffic shaping is
usually applied in the outbound direction of a port.
z
Congestion management provides a resource scheduling policy to arrange the forwarding
sequence of packets when congestion occurs. Congestion management is usually applied in the
outbound direction of a port.
