However, the Inter-Serv model imposes extremely high requirements on devices. In a network with
heavy data traffic, the Inter-Serv model imposes very great pressure on the storage and processing
capabilities of devices. On the other hand, the Inter-Serv model is poor in scalability, and therefore, it is
hard to be deployed in the core Internet network.
DiffServ Service Model
DiffServ is a multiple services model that can satisfy diverse QoS requirements. Unlike IntServ, DiffServ
does not require an application to signal the network to reserve resources before sending data. DiffServ
is easy to implement and extend.
All QoS techniques mentioned in this document are based on the Diff-Serv model.
QoS Techniques Overview
The QoS techniques include traffic classification, traffic policing, traffic shaping, line rate, congestion
management, and congestion avoidance. The following part briefly introduces these QoS techniques.
Positions of the QoS Techniques in a Network
Figure 1-1 Positions of the QoS techniques in a network
As shown in
and congestion avoidance mainly implement the following functions:
Traffic classification uses certain match criteria to organize packets with different characteristics
into different classes. Traffic classification is the basis for providing differentiated services.
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.
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. Traffic shaping is usually applied to
the outgoing traffic of a port.
Congestion management provides a resource scheduling policy to arrange the forwarding
sequence of packets when congestion occurs. Congestion management is usually applied to the
outgoing traffic of a port.
1-1, traffic classification, traffic shaping, traffic policing, congestion management,