HP HP 830 Series, Configuration Manual

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Configuring QoS
Overview
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. The
amount of resources the packets can obtain completely depends on the time they arrive. This service is
called "best-effort." It delivers packets to their destinations in the most effective method, without any
guarantee for such issues as delay, jitter, and packet loss ratio.
This service policy is only suitable for applications insensitive to bandwidth and delay, such as Word
Wide Web (WWW) and email.
QoS requirements of new applications
Besides traditional applications such as WWW, email and FTP, network users are implementing 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 example, to access the database of the company or to monitor
remote devices through Telnet).
These new applications have special requirements for bandwidth, delay, and jitter. For example,
videoconference and VoD require high bandwidth, low delay, and low jitter. Mission-critical applications,
such as transactions and Telnet, may not require high bandwidth but require low delay and preferential
service during congestion.
The emerging applications require higher service performance of IP networks. Required network services
during packet forwarding include providing dedicated bandwidth, reducing packet loss ratio, managing
and avoiding congestion, and regulating network traffic. To meet these requirements, networks must
provide improved services.
Congestion: causes, impacts, and countermeasures
Network congestion is a major factor contributing to degradation of service quality on a traditional
network. Congestion is a situation where the forwarding rate decreases due to insufficient resources,
resulting in extra delay.
Causes
Congestion occurs in complex packet switching circumstances in the Internet. Figure 476 shows two
common cases: