H3C Technologies H3C WX6000 Series Access Controllers - Manual (Page 424)

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QoS Overview
The term switch in this document refers to a switch in a generic sense or an access controller
configured with the switching function unless otherwise specified.
Introduction
Quality of Service (QoS) is a concept generally existing in occasions where service supply-demand
relations exist. QoS measures the ability to meet the service needs of customers. Generally, the
evaluation is not to give precise grading. The purpose of the evaluation is to analyze the conditions
where the services are good and the conditions where the services still need to be improved, so that
specific improvements can be implemented.
In Internet, QoS measures the ability of the network to deliver packets. The evaluation on QoS can be
based on different aspects because the network provides diversified services. Generally speaking, QoS
is the evaluation on the service ability to support the critical indexes such as delay, delay jitter and
packet loss rate in packet delivery.
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, FTP and E-mail.
New Requirements Brought forth by New Services
With the fast development of computer networks, more and more networks are connected into Internet.
Internet extends very quickly in scale, coverage and the number of users. More and more users use the
Internet as a platform for data transmission and develop various applications on it.
Besides traditional applications such as WWW, FTP, and E-mail, Internet users also try to develop new
services on Internet, such as tele-education, tele-medicine, video phones, video conferencing, and
video on demand (VOD). Enterprise users also hope to connect their branch offices in different