17 – Quality Of Service

Mo7sin 17/02/2012 781 3,910 views

Quality of Service Overview

This chapter explains quality of service (QoS) and the service models that embody it. It also suggests benefits you can gain from implementing Cisco IOS QoS in your network. Then it focuses on the Cisco IOS QoS features and the technologies that implement them.

To identify the hardware platform or software image information associated with a feature, use the Feature Navigator on Cisco.com to search for information about the feature or refer to the software release notes for a specific release. For more information, see the “Identifying Supported Platforms” section in the “Using Cisco IOS Software” chapter in this book.

What Is Quality of Servic

QoS refers to the ability of a network to provide improved service to selected network traffic over various underlying technologies including Frame Relay, ATM, Ethernet and 802.1 networks, SONET, and IP-routed networks. In particular, QoS features provide improved and more predictable network service by providing the following services

Supporting dedicated bandwidth

Improving loss characteristics

Avoiding and managing network congestion

Shaping network traffic

Setting traffic priorities across the network

About QoS Architectur

You configure QoS features throughout a network to provide for end-to-end QoS delivery. The following three components are necessary to deliver QoS across a heterogeneous network:

QoS within a single network element, which includes queueing, scheduling, and traffic shaping features.

QoS signalling techniques for coordinating QoS for end-to-end delivery between network elements.

QoS policing and management functions to control and administer end-to-end traffic across a network.

Not all QoS techniques are appropriate for all network routers. Because edge routers and backbone routers in a network do not necessarily perform the same operations, the QoS tasks they perform might differ as well. To configure an IP network for real-time voice traffic, for example, you would need to consider the functions of both edge and backbone routers in the network, then select the appropriate QoS feature or features

In general, edge routers perform the following QoS functions:

Packet classification

Admission control

Configuration management

In general, backbone routers perform the following QoS functions

Congestion management

Congestion avoidance


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  1. Alexis Isaacson 22/04/2012 at 5:35 AM -

    This is one awesome post.Much thanks again. Great.

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