R3166-R3206-HP High-End Firewalls Network Management Configuration Guide-6PW101

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QoS
Overview
Introduction to QoS
In data communications, Quality of Service (QoS) is the ability of a network to provide differentiated
service guarantees for diversified traffic in terms of bandwidth, delay, jitter, and drop rate.
Network resources are scarce. The contention for resources requires that QoS prioritize important traffic
flows over trivial ones. For example, in the case of fixed bandwidth, if a traffic flow gets more bandwidth,
the other traffic flows will get less bandwidth and may be affected. When making a QoS scheme, you
must consider the characteristics of various applications to balance the interests of diversified users and
to utilize network resources.
Traditional packet forwarding services
On traditional IP networks, devices treat all packets equally and handle them using the first in first out
(FIFO) policy. All packets share the resources of the network and devices. How many resources the
packets can obtain completely depends on the time they arrive. This service is called best-effort. It
delivers packets to their destinations as possibly as it can, without any guarantee for delay, jitter, packet
loss ratio, or reliability.
This service policy is only suitable for applications insensitive to bandwidth and delay, such as WWW,
file transfer and e-mail.
New requirements from emerging applications
The Internet has been growing along with the fast development of networking technologies. More and
more users take the Internet as their data transmission platform to implement various applications.
Besides traditional applications such as WWW, e-mail and FTP, network users are experiencing new
services, such as tele-education, telemedicine, video telephone, videoconference and Video-on-Demand
(VoD). The enterprise users expect to connect their regional branches together through VPN technologies
to carry out operational applications, for instance, to access the database of the company or to monitor
remote devices through Telnet.
These new applications have one thing in common, that is, they all have special requirements for
bandwidth, delay, and jitter. For instance, videoconference and VoD require large bandwidth, low delay
and jitter. As for mission-critical applications such as business transactions and Telnet, they may not
require as large bandwidth but do require low delay and preferential service during congestion.
The emerging applications demand higher service performance of IP networks. Better network services
during packets forwarding are required, such as providing dedicated bandwidth, reducing packet loss
ratio, managing and avoiding congestion, regulating network traffic, and setting the precedence of
packets. To meet these requirements, networks must provide more improved services.