Configuring QoS

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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 might 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 email.

QoS requirements of new applications

The Internet has been growing along with the fast development of networking technologies.

Besides traditional applications such as WWW, email 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 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 might not require high 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, and regulating network traffic. To meet these requirements, networks must provide more improved services.

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