Related Certifications: CCIP, CCVP, IP Telephony Specialists Certifications.

Number of Questions: 45-55 Duration: 90 minutes

Exam Topics Include:

* IP QoS Fundamentals and Best Practices
* IP QoS Components
* Modular QoS CLI and Auto-QoS
* Classification and Marking
* Congestion Management and Avoidance Methods
* Traffic Policing and Shaping
* Link Efficiency Mechanisms

The QOS exam is one of the qualifying exams for the Cisco Certified Internetwork Professional, Cisco Certified Voice Professional, Cisco IP Telephony Design Specialist, Cisco IP Telephony Express Specialist, Cisco IP Telephony Operations Specialist, and Cisco IP Telephony Support Specialist certifications. The exam will certify that the successful candidate has knowledge and skills necessary to configure and troubleshoot Cisco IOS routers running Quality of Service protocols in Service Provider and Enterprise environments. The importance of this exam is evident in the fact that it applies to so many different certifications.

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QUESTION 1
Which of the following markers can be set by Committed Access Rate (CAR)? (Choose all
that apply.)
A. DSCP bits
B. QoS Group
C. ATM CLP bit
D. Frame Relay DE bit
E. IP precedence bits
Answer: A, B, E

What makes the DiffServ model more scalable than the IntServ model? (Choose all that
apply.)
A. DiffServ makes use of per-aggregate QoS instead of per-flow QoS.
B. DiffServ makes use of hop-by-hop signaling which allows DiffServ to scale to a larger
number of application flows.
C. DiffServ is capable of implementing admission control either locally on the routers or be
offloaded to a central policy server using the COPS protocol.
D. DiffServ routers are not compelled to track the state information for each individual flow.
Answer: A, D
The newly appointed Chinatag trainee technician wants to know what the benefits of
using traffic shaping to implement network rate limiting is.What will your reply be?
(Choose all that apply.)
A. Traffic shaping is an effective tool for rate-limiting VoIP traffic. B.
It will not increase packet loss.
C. It will not add to packet transit delays.
D. Traffic shaping can interact with congestion mechanisms embedded in Frame Relay. E.
Traffic shaping can be used on inbound and outbound traffic on a router.
Answer: B, D
Incorrect:
A. Shaping adds variable delay to traffic, possibly causing jitter C.
A shaper typically delays excess traffic using a buffer
E. This is a feature of policing
Study the Exhibit below carefully:
Router# show interfaces hssi 0/0/0 rate-limit
Hssi0/0/0 45Mbps to R1
Input
matches: all traffic
params: 20000000 bps, 24000 limit, 24000 extended limit
conformed 8 packets, 428 bytes; action: transmit
exceed 0 packets, 0 bytes; action: drop
last packet: 8680ms ago, current burst: 0 bytes
last cleared 00:03:59 ago, conformed 0 bps, exceed 0 bps
Output
matches: all traffic
params: 20000000 bps, 24000 limit, 24000 extended limit
conformed 0 packets, 0 bytes; action: transmit
exceed 0 packets, 0 bytes; action; drop
last packet: 8680ms ago, current burst: 0 bytes
last cleared 00:03:59 ago, conformed 0 bps, exceed 0 bps
According to the exhibit, the router has been configured with Committed Access
Rate (CAR) to rate limit traffic.
What data rate has the traffic been limited to?
A. 192 Kbps
B. 2400 Kbps
C. 4,5 Mbps
D. 20 Mbps
E. 40 Mbps
Answer: D
The newly appointed Chinatag trainee technician wants to know which type of software
queuing mechanism is Frame Relay Traffic Shaping implemented with on the physical
interface. What will your reply be?
A. Priority Queuing (PQ)
B. Custom Queuing (CQ)
C. FIFO
D. Weighted Fair Queuing (WFQ)
E. IP Real Time Transport Protocol (RTP) Priority
Answer: D
Why is it beneficial to make use of Enhanced LMI (ELMI) on Cisco networks?
A. ELMI is responsible for providing virtual provisioning tools at the edge of the Frame
Relay network.
B. ELMI permits routers to dynamically download QoS information from Cisco switches for
use in traffic shaping or for congestion management purposes.
C. ELMI provides the router the ability to use additional QoS tools including rate limiting
with CAR and the Modular QoS Command Line Interface (MQC).
D. ELMI allows the router to deliver packets at the line rate of the Frame Relay interface,
regardless of the condition of the Frame Relay network.
Answer: B
Which of the following statements are true when you compare DSCP and IP
Precedence to each other? (Choose all that apply.)
A. DSCP is backwards compatible with IP Precedence.
B.
DSCP cannot be easily mapped into QoS because of its expanded classification options. C.
DSCP is more granular the IP Precedence, since more marking combinations are available.
D. DSCP appears stubby when compared IP Precedence, since devices make use of
DSCP as defined in RFC exclusively.
E. DSCP is 6 bits long and IP Precedence is 3 bits long.
F. DSCP is more restrictive than IP Precedence, since devices are only allowed to use
DSCP as defined in RFCs.
Answer: A, C, E
Explanation:
A)DSCP is backward compatible with IP Precedence (Class Selector Code point, RFC
1812) but not with the ToS byte definition from RFC 791 (”DTR” bits)
Reference: Introduction to IP QoS (Course) p.45
Which MQC command would you use to perform marking properly?
A. precedence 5
B. ip precedence 5
C. set ip precedence 5
D. set ip mark precedence 5
E. mark ip precedence 5
Answer: C
Explanation:
IP precedence is encoded into the three high-order bits of the ToS field in the IP header. It
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Are you ready to take the QOS, CVOICE, or CIPT exam for the Cisco IP Telephony certification? You learned the concepts, you have the experience to put them into real-world use, and now you want to practice, practice, practice until exam time. Cisco IP Telephony Flash Cards and Exam Practice Pack gives you three methods of proven, late-stage Cisco IP Telephony exam preparation in one package.

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All exam topics are included in 100+ graphical quick reference sheets.

Cisco IP Telephony Flash Cards and Exam Practice Pack is part of a recommended learning path from Cisco Systems that includes simulation and hands-on training from authorized Cisco Learning Partners and self-study products from Cisco Press. To find out more about instructor-led training, e-learning, and hands-on instruction offered by authorized Cisco Learning Partners worldwide, please visit www.cisco.com/go/authorizedtraining.

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The networks of yesteryear physically separated voice, video, and data traffic. Literally, these traffic types flowed over separate media (for example, leased lines or fiber-optic cable plants). Today, however, network designers are leveraging the power of the data network to transmit voice and video, thus achieving significant cost savings by reducing equipment, maintenance, and even staffing costs.

The challenge, however, with today’s converged networks is that multiple applications are contending for bandwidth, and some applications such as, voice can be more intolerant of delay (that is, latency) than other applications such as, an FTP file transfer. A lack of bandwidth is the overshadowing issue for most quality problems.

When a lack of bandwidth exists, packets can suffer from one or more of the following symptoms:

*

Delay—Delay is the time that is required for a packet to travel from its source to its destination. You might witness delay on the evening news, when the news anchor is talking through satellite to a foreign news correspondent. Because of the satellite delay, the conversation begins to feel unnatural.
*

Jitter—Jitter is the uneven arrival of packets. For example, consider that in a Voice over IP (VoIP) conversation, packet 1 arrives. Then, 20 ms later, packet 2 arrives. After another 70 ms, packet 3 arrives, and then packet 4 arrives 20 ms behind packet 3. This variation in arrival times (that is, variable delay) is not dropping packets, but this jitter can be interpreted by the listener as dropped packets.
*

Drops—Packet drops occur when a link is congested and a buffer overflows. Some types of traffic, such as User Datagram Protocol (UDP) traffic (for example, voice), are not retransmitted if packets are dropped.

Fortunately, quality of service (QoS) features that are available on Cisco routers and switches can recognize your “important” traffic and then treat that traffic in a special way. For example, you might want to allocate 128 kbps of bandwidth for your VoIP traffic and also give that traffic priority treatment.

Consider water that is flowing through a series of pipes with varying diameters. The water’s flow rate through those pipes is limited to the water’s flow rate through the pipe with the smallest diameter. Similarly, as a packet travels from its source to its destination, its effective bandwidth is the bandwidth of the slowest link along that path.

Figure 1Figure 1

Because your primary challenge is a lack of bandwidth, the logical question is, “How do you increase available bandwidth?” A knee-jerk response to that question is often, “Add more bandwidth.” Although adding more bandwidth is the best solution, it comes at a relatively high cost.

Compare your network to a highway system in a large city. During rush hour, the lanes of the highway are congested, but the lanes can be underutilized during other periods of the day. Instead of just building more lanes to accommodate peak traffic rates, the highway engineers add carpool lanes. Cars with two or more riders can use the reserved carpool lane. These cars have a higher priority on the highway. Similarly, you can use QoS features to give your mission-critical applications higher-priority treatment in times of network congestion.

Some of the QoS features that can address issues of delay, jitter, and packet loss include the following:

*

Queuing—Queuing can send higher-priority traffic ahead of lower-priority traffic and make specific amounts of bandwidth available for those traffic types. Examples of queuing strategies that you consider later in these Quick Reference Sheets include the following:
o

Priority Queuing (PQ)
o

Custom Queuing (CQ)
o

Modified Deficit Round Robin (MDRR) queuing
o

Weighted Fair Queuing (WFQ)
o

Class-Based WFQ (CB-WFQ)
o

Low Latency Queuing (LLQ)
*

Compression—By compressing a packet’s header or payload, fewer bits are sent across the link. This effectively gives you more bandwidth.

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ISBN: 1-58705-320-9

As a final preparation tool providing a review of QOS exam topics, the CCVP QOS Quick Reference Sheets complement official Cisco curriculum, other books, or other exam preparatory material. This digital Short Cut provides readers with detailed, graphical-based information, highlighting the key topics on the latest QOS exam in a quick-review format. These fact-filled Quick Reference Sheets allow certification candidates to get all-important information at a glance, helping them to focus their study on areas of weakness and to enhance memory retention of important concepts.

The CCVP certification recognizes a candidate’s ability to create an IP telephony solution that is transparent, scalable, and manageable. Earning a CCVP certification validates a robust set of skills in implementing, operating, configuring, and troubleshooting a converged IP network. The certification content focuses on Cisco Systems Unified CallManager, quality of service (QoS), gateways, gatekeepers, IP phones, voice applications, and utilities on Cisco routers and Cisco Catalyst switches.

The QOS exam is one of the qualifying exams for the CCIP and CCVP, and it certifies that the successful candidate has knowledge and skills necessary to configure and troubleshoot Cisco IOS routers running QoS protocols in service provider and enterprise environments. The exam covers topics on IP QOS, classification and marking mechanisms, queuing mechanisms, traffic shaping and policing mechanisms, congestion avoidance mechanisms, link efficiency mechanisms, modular QOS command-line interface, and QOS Best Practices.

This Short Cut is derived from the print publication, Cisco IP Telephony Flash Cards and Exam Practice Pack, ISBN: 1-58720-128-3.

Table of Contents:

Why You Need Quality of Service (QoS)

QoS Basics

QoS Deployment

QoS Components

Basic QoS Configuration

Traffic Classification and Marking

Queuing

Weighted Random Early Detection (WRED)

Traffic Conditioners

QoS on Slow-Speed Links

QoS Design Guidelines

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* QoS concepts, tools, and architectures
* Modular QoS CLI (MQC), QoS Policy Manager (QPM), and AutoQoS
* Classification and marking
* Congestion management
* Traffic shaping and policing
* Congestion avoidance through drop policies
* Compression tools and link fragmentation and interleaving (LFI) tools for link efficiency
* LAN QoS
* QoS best practices

The CCVP certification validates a robust set of skills in implementing, operating, configuring, and troubleshooting a converged IP network. A solid understanding of quality-of-service (QoS) features and implementation is essential for CCVP certification and is also a core component of the CCIP® certification.

Cisco QOS Exam Certification Guide, Second Edition, is a best-of-breed Cisco® exam study guide that focuses specifically on the objectives for the QOS 642-642 exam. Senior instructor and best-selling author Wendell Odom and senior AVVID consultant Michael Cavanaugh share preparation hints and test-taking tips, helping you identify areas of weakness and improve your QoS knowledge. Material is presented in a concise manner, focusing on increasing your understanding and retention of exam topics.

Cisco QOS Exam Certification Guide, Second Edition, presents you with an organized test preparation routine through the use of proven series elements and techniques. “Do I Know This Already?” quizzes open each chapter and allow you to decide how much time you need to spend on each section. Exam topic lists and Foundation Summary tables, figures, and snapshot information make referencing easy and give you a quick refresher whenever you need it. Challenging chapter-ending review questions help you assess your knowledge and reinforce key concepts. The companion CD-ROM contains a powerful testing engine that allows you to focus on individual topic areas or take complete, timed exams. The assessment engine also tracks your performance and provides feedback on a module-by-module basis, presenting question-by-question remediation to the text. Well-regarded for its level of detail, assessment features, and challenging review questions and exercises, this book helps you master the concepts and techniques that will enable you to succeed on the exam the first time.

Cisco QOS Exam Certification Guide, Second Edition, is part of a recommended learning path from Cisco Systems® that includes simulation and hands-on training from authorized Cisco Learning Partners and self-study products from Cisco Press. To find out more about instructor-led training, e-learning, and hands-on instruction offered by authorized Cisco Learning Partners worldwide, please visit www.cisco.com/go/authorizedtraining.

Companion CD-ROM

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This volume is part of the Exam Certification Guide Series from Cisco Press®. Books in this series provide officially developed exam preparation materials that offer assessment, review, and practice to help Cisco Career Certification candidates identify weaknesses, concentrate their study efforts, and enhance their confidence as exam day nears.

This chapter covers the following exam topics specific to the QoS exam:

*

Given a network requiring QoS, explain how to implement a QoS policy using MQC
*

Explain how AutoQoS is used to implement QoS policy

Most of the topics covered in Chapters 1, “QoS Overview,” and 2, “QoS Tools and Architectures,” can apply to a network that uses equipment from most any manufacturer. Sure, there were some specifics about Cisco IOS QoS tools and about Cisco IP Phones, but all the concepts about QoS architectures and traffic characteristics of voice, video, and data apply to any network, regardless of manufacturer.

This chapter is specific about discussing several tools available only for Cisco products. Most of the more modern QoS tools from Cisco use configuration commands that conform to a convention called the Modular QoS CLI (MQC), which significantly reduces the complexity of QoS configuration as compared to QoS tools that don’t use MQC commands. Frankly, before MQC, QoS configuration was one of the more challenging things to configure in Cisco IOS Software. With MQC, most of the complexity has been removed.

Although easier configuration of a router or switch using MQC is indeed wonderful, MQC enables a couple of other important Cisco QoS tools. Cisco offers a management application called QoS Policy Manager (QPM), which provides a web browser interface to network engineers, allowing them to easily define QoS policies for a network, all with intuitive pointing and clicking. QPM can baseline the network’s QoS performance, configure the routers and switches based on the policy, measure the ensuing performance, and monitor the configurations to make sure no one changes the QoS configuration.

Compared to the old days, MQC makes it easier to configure each device, and QPM makes it easier to configure and monitor QoS for an entire network.

In addition, Cisco offers a tool called AutoQoS in Cisco IOS Release 12.3 mainline router and Cisco IOS Release 12.1EA 2950 switch. (Go to http://www.cisco.com/go/fn to use the Cisco Feature Navigator to find more specific information about AutoQoS support on different platforms.) AutoQoS allows a network engineer to configure a single device with just a few generic commands, and the device automatically configures all the appropriate QoS tools. So, even without QPM, a network engineer can configure QoS with confidence. Also, the automatically generated configuration can be changed, if the default settings are not quite what the engineer wants.

MQC, QPM, and AutoQoS provide some fantastic advantages. In this chapter, you’ll read about all three. After that, Chapters 4 through 9 take a closer look at six categories of QoS tools available in Cisco routers.
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