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Introduction to
Quality of Service
Introduction to
Quality of Service
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Objectives
Objectives
Upon completion of this module, you will be
able to perform the following tasks:
• Explain the significance of Quality of Service (QoS)
• Describe new Quality of Service (QoS) features in
Cisco IOS 12.1
• Explain which problems QoS solves
The purpose of this module is to quickly survey the new Quality of Service (QoS)
features in Cisco IOS 12.1 and to describe the problems they solve..
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Topics
Topics
QoS overview
New QoS features
Quick look at Diff Serv framework
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Why Is QoS So Important?

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Where Do We Use QoS?
Where Do We Use QoS?
Low bandwidth links
Managing bandwidth
Application service levels
• Voice
• Mission-critical applications
IP network replacing ATM infrastructure
Differentiated levels of service
Internet
The slide lists some of the places where QoS is being applied today.
QoS is important to those using low bandwidth links, to protect voice or
mission-critical traffic on those links, especially in the event of congestion. Control
and protection of voice and mission-critical traffic can also be important to the
customer over higher speed links.
Sometimes QoS is desired because IP networking is replacing ATM, and QoS is
something valuable that ATM has to offer, and the customer wishes to also have
comparable capabilities with IP networking.
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What Is QoS?
What Is QoS?
QoS:
• Allows a network to provide better
service to selected traffic
• Enables the network to handle both

User
Home
User
Hunt
Group
Network
Management
FR, xDSL
Small
Office
Hosting
PSTN
Internet
AAA
Backbone
Access
Customer Premises
Equipment
Distribution Layer
or PoP
Determine policy and service levels
implementation:
• Classifying
• Marking
• Policing /
Shaping
• Queuing /
Scheduling
• Congestion
Avoidance

• Finer granularity and scalability
• Modular QoS Command Line Interface (CLI)
is easier to use
Class-Based Weighted Fair Queuing (CBWFQ) allows the user to define traffic classes based on
customer-defined match criteria such as access control lists (ACLs), input interfaces, protocol, and
QoS label. For example, a class might consist of a team working on a certain project or a class can
be created for the important mission-critical applications, for example, enterprise resources
planning (ERP). When the traffic classes have been defined, they can be assigned a bandwidth,
queue limit, or drop policy such as Weighted Random Early Detection (WRED).
• Bandwidth allocation —CBWFQ allows you to specify the exact amount of bandwidth to be
allocated for a specific class of traffic. Accounting for available bandwidth on the interface,
you can configure up to 64 classes.
• Finer granularity and scalability—CBWFQ allows you total flexibility to define a class based
on ACLs and protocols or input interfaces, thereby providing finer granularity.
• Support in the modular command-line interface (CLI) framework—CBWFQ is supported in the
new modular CLI framework, which is a new, template-based CLI. This new modular CLI
eases the configuration of CBWFQ by introducing the class-map, service-map and policy-map
approach. This “virtual template” eases the constant configuration of policies per interface, and
reduces the configuration by allowing the service maps to be assigned to each interface –
without reconfiguring the match criteria/ACLs and policies.
• WRED supported as a drop policy—CBWFQ supports WRED as a drop policy per class, thus
allowing you to provide differentiated service within a class.
This feature is supported on all platforms that WFQ is supported on, in other words, the Cisco 7200,
4700, 4500, 3600, and 2600 series, and so on.
First appearance in a Cisco IOS software T release: 12.0(5)T.
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IP Real-Time Transport
Protocol (RTP) Priority

the data fragments, thus ensuring that voice traffic is serviced with minimal delay.
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