H3C S5810 Series, Руководство по эксплуатации

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QoS Overview
This chapter covers the following topics:
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Introduction to QoS
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Networks Without QoS Guarantee
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QoS Requirements of New Applications
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Congestion: Causes, Impacts, and Countermeasures
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QoS Technology Implementations
Introduction to QoS
Quality of Service (QoS) reflects the ability of a network to meet customer needs. In an internet, QoS
evaluates the ability of the network to forward packets of different services.
The evaluation can be based on different criteria because the network may provide various services.
Generally, QoS performance is measured with respect to bandwidth, delay, jitter, and packet loss ratio
during packet forwarding process.
Networks Without QoS Guarantee
On traditional IP networks without QoS guarantee, 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, and so on.
This service policy is only suitable for applications insensitive to bandwidth and delay, such as Word
Wide Web (WWW) and E-Mail.
QoS Requirements of New Applications
The Internet has been growing along with the fast development of networking technologies.
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). Enterprise users expect to connect their regional branches together with 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 example, videoconference and VoD require high bandwidth, low delay
and jitter. As for mission-critical applications, such as transactions and Telnet, they may not require high
bandwidth but do require low delay and preferential service during congestion.