Transcript CCNP-IV-ONT_Mod_3_Lesson_2

Optimizing Converged
Cisco Networks (ONT)
Module 3: Introduction to IP QoS
© 2006 Cisco Systems, Inc. All rights reserved.
Lesson 3.2:
Implementing Cisco
IOS QoS
© 2006 Cisco Systems, Inc. All rights reserved.
Objectives
 Describe the need for QoS as it relates to various types
of network traffic.
 Identify QoS mechanisms.
 Describe the steps used to implement QoS.
© 2006 Cisco Systems, Inc. All rights reserved.
What Is Quality of Service?
Two Perspectives
 The user perspective
Users perceive that their applications are
performing properly
Voice, video, and data
 The network manager perspective
Need to manage bandwidth allocations
to deliver the desired application
performance
Control delay, jitter, and
packet loss
© 2006 Cisco Systems, Inc. All rights reserved.
Different Types of Traffic Have Different
Needs
 Real-time applications especially
sensitive to QoS
Application
Examples
Delay
Jitter
Packet
Loss
Interactive Voice
and Video
Y
Y
Y
Streaming Video
N
Y
Y
Transactional/
Interactive
Y
N
N
Bulk Data
Email
File Transfer
N
N
N
Interactive voice
Videoconferencing
 Causes of degraded performance
Congestion losses
Sensitivity to
QoS Metrics
Variable queuing delays
 The QoS challenge
Manage bandwidth allocations to
deliver the desired application
performance
Control delay, jitter, and packet
loss
© 2006 Cisco Systems, Inc. All rights reserved.
Need to manage
bandwidth allocations
Cisco IOS QoS Tools
 Congestion management:
PQ
CQ
WFQ
CBWFQ
 Queue management
WRED
 Link efficiency
Link fragmentation and interleave
RTP and CRTP
 Traffic shaping and traffic policing
© 2006 Cisco Systems, Inc. All rights reserved.
QoS Toolbox
Priority Queuing
PQ puts data into four levels of queues: high, medium,
normal, and low.
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Custom Queuing
CQ handles traffic by assigning a specified amount of queue space to each class of
packet and then servicing up to 17 queues in a round-robin fashion.
© 2006 Cisco Systems, Inc. All rights reserved.
Weighted Fair Queuing
•WFQ makes the transfer rates and interarrival periods of active high-volume conversations much
more predictable.
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Weighted Random Early Detection
•WRED provides a method that stochastically discards packets if congestion begins to increase.
© 2006 Cisco Systems, Inc. All rights reserved.
© 2006 Cisco Systems, Inc. All rights reserved.
Implementing QoS
Step 1: Identify types of traffic and
their requirements.
Step 2: Divide traffic into classes.
Step 3: Define QoS policies for
each class.
© 2006 Cisco Systems, Inc. All rights reserved.
Step 1: Identify Types of Traffic and Their
Requirements
 Network audit: Identify traffic on the network.
 Business audit: Determine how important each type of
traffic is for business.
 Service levels required: Determine required response
time.
© 2006 Cisco Systems, Inc. All rights reserved.
Step 2: Define Traffic Classes
Scavenger
Class
© 2006 Cisco Systems, Inc. All rights reserved.
Less than
Best Effort
Step 3: Define QoS Policy
 A QoS policy is a
network-wide definition of
the specific levels of QoS
that are assigned to
different classes of
network traffic.
© 2006 Cisco Systems, Inc. All rights reserved.
Quality of Service Operations
How Do QoS Tools Work?
Classification
and Marking
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Queuing and
(Selective) Dropping
Post-Queuing
Operations
Self Check
1. What types of applications are particularly sensitive to
QoS issues?
2. What is WFQ? How is it different than FIFO?
3. What are the 3 basic steps involved in implementing
QoS?
4. What is Scavenger Class?
© 2006 Cisco Systems, Inc. All rights reserved.
Summary
 QoS is important to both the end user and the network
administrator. End users experience lack of QoS as
poor voice quality, dropped calls or outages.
 Network traffic differs in its ability to handle delay, jitter
and packet loss. Traffic sensitive to these issues
requires priority treatment. QoS measures can provide
priority to sensitive traffic, while still providing services
to more resilient traffic.
 Implementing QoS involves 3 basic steps: identify the
types of traffic on your network, divide the traffic into
classes, and define a QoS policy for each traffic class.
© 2006 Cisco Systems, Inc. All rights reserved.
Q and A
© 2006 Cisco Systems, Inc. All rights reserved.
Resources
 QoS Best Practices At-A-Glance
http://www.cisco.com/application/pdf/en/us/guest/tech/tk759/c14
82/cdccont_0900aecd80295aa1.pdf
 QoS Tools At-A-Glance
http://www.cisco.com/application/pdf/en/us/guest/tech/tk759/c14
82/cdccont_0900aecd80295abf.pdf
© 2006 Cisco Systems, Inc. All rights reserved.
© 2006 Cisco Systems, Inc. All rights reserved.