Diffserv Service Model; Qos Techniques Overview; Positions Of The Qos Techniques In A Network - 3Com 4510G Configuration Manual

requested, reserved, and pre-purchased resources. The Inter-Serv model can definitely identify and
guarantee QoS for each data flow, and provides the most granularly differentiated QoS.
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 Figure
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 and congestion. Traffic shaping is
usually applied to the outgoing traffic of a port.
1-1, traffic classification, traffic shaping, traffic policing, congestion management,
1-2