3Com 4500 1

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1 QoS Configuration

When configuring QoS, go to these sections for information you are interested in:

z Overview

z QoS Supported By Switch 4500 Series

z QoS Configuration

z Displaying and Maintaining QoS

z QoS Configuration Examples

Overview

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 solving the core issues such as delay,

jitter, and packet loss ratio in the packet forwarding process.

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, E-mail and FTP.

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