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1 QoS Configuration
Overview
Introduction to QoS
Quality of Service (QoS) is a concept concerning service demand and supply. It reflects the ability to
meet customer needs. Generally, QoS does not focus on grading services precisely, but on improving
services under certain conditions.
In an internet, QoS refers to the ability of the network to forward packets. The evaluation on QoS of a
network can be based on different aspects because the network may provide various services.
Generally, QoS refers to the ability to provide improved service by addressing the essential issues such
as delay, jitter, and packet loss ratio in the packet forwarding process.
Traditional Packet Forwarding Service
In traditional IP networks, packets are treated equally. That is, the FIFO (first in first out) policy is
adopted for packet processing. Network resources required for packet forwarding is determined by the
order in which packets arrive. All the packets share the resources of the network. Network resources
available to the packets completely depend on the time they arrive. This service policy is known as
Best-effort, which delivers the packets to their destination with the best effort, with no assurance and
guarantee for delivery delay, jitter, packet loss ratio, reliability, and so on.
The traditional Best-Effort service policy is only suitable for applications insensitive to bandwidth and
delay, such as WWW, file transfer and E-mail.
New Applications and New Requirements
With the expansion of computer network, more and more networks become part of the Internet. The
Internet gains rapid development in terms of scale, coverage and user quantities. More and more users
use the Internet as a platform for their services and for data transmission.
Besides the traditional applications such as WWW, E-mail, and FTP, new services are developed on the
Internet, such as tele-education, telemedicine, video telephone, videoconference and
Video-on-Demand (VoD). Enterprise users expect to connect their regional branches together using
VPN techniques for coping with daily business, for instance, accessing databases or manage remote
equipments through Telnet.
All these new applications have one thing in common, that is, they have special requirements for
bandwidth, delay, and jitter. For instance, bandwidth, delay, and jitter are critical for videoconference
and VoD. As for other applications, such as transaction processing and Telnet, although bandwidth is
not as critical, a too long delay may cause unexpected results. That is, they need to get serviced in time
even if congestion occurs.
Newly emerging applications demand higher service performance from IP networks. In addition to
simply delivering packets to their destinations, better network services are demanded, such as
allocating dedicated bandwidth, reducing packet loss ratio, avoiding congestion, regulating network
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