Pass4sure Cisco Certification

Quality of Service Exam

Exam Number: 642-642
Associated Certifications: CCIP, CCVP, IP Telephony Design Specialist, IP Telephony Express Specialist, IP Telephony Operations Specialist, and IP Telephony Support Specialist
Duration: 90 minutes (45-55 questions)
Available Languages: English
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Exam Description Exam Topics Recommended Training Additional Resources
Exam Description
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 QOS 642-642 exam will test materials covered under the Implementing Cisco Quality of Service QOS v2.1 course. 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 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.

Exam Topics
The following information provides general guidelines for the content likely to be included on the exam. However, other related topics may also appear on any specific delivery of the exam.

IP QoS Fundamentals
Given a description of a converged network, identify problems that could lead to poor quality of service and explain how the problems might be resolved
Define the term Quality of Service (QoS) and identify and explain the key steps to implementing QoS on a converged network

IP QoS Components
List and explain the models for providing Quality of Service on a network
Explain the purpose and function of the DiffServ model
Describe the basic format of and explain the purpose of the DSCP field in the IP header
Define and explain the different per hop behaviors used in DSCP
Explain the interoperability between DSCP-based and IP-precedence-based devices in a network
Given a list of QoS actions, correctly match the QoS actions to mechanisms for implementing QoS and identify where in a network the different QoS mechanisms are commonly used

Modular QoS CLI and Auto-QoS
Given a network requiring QoS, explain how to implement a QoS policy using MQC
Explain how AutoQoS is used to implement QoS policy

Classification and Marking
Explain how link layer and network layer markings are used to define service classes and the different applications represented by each of these service classes
Given a network and a description of QoS issues, use MQC CLI commands to classify packets
Given a network and a description of QoS issues, use class-based marking to assign packets to a specific service class
Describe the function of Network Based Application Recognition
Describe the purpose of pre-classification to support QoS in various VPN (IPSEC, GRE, L2TP) configurations
Describe QoS trust boundaries and their significance in LAN based classification and marking
Identify the different classification and marking options available on Cisco L2 and L3 switching platforms

Congestion Management Methods
List and explain the different queuing algorithms
Explain the components of hardware and software queuing systems on Cisco routers and how they are effected by tuning and congestion
Describe the benefits and drawbacks of using WFQ to implement QoS
Explain the purpose and features of Class-Based WFQ (CBWFQ)
Explain the purpose and features of Low Latency Queuing (LLQ)
Identify the Cisco IOS commands required to configure and monitor LLQ on a Cisco router
Describe and explain the different queuing capabilities available on the Cisco Catalyst 2950 Switch

Congestion Avoidance Methods
Describe the drawbacks tail drop as a congestion control mechanism
Describe the elements of a RED traffic profile
Describe Weighted Random Early Detection and how it can be used to prevent congestion
Identify the Cisco IOS commands required to configure and monitor DSCP-based CB-WRED
Explain how ECN interacts with WRED in Cisco IOS

Traffic Policing and Shaping
Describe the purpose of traffic conditioning using traffic policing and traffic shaping and differentiate between the features of each
Explain how network devices measure traffic rates using single rate or dual rate, single or dual token bucket mathematical models
Identify the Cisco IOS commands required to configure and monitor single rate and dual rate CB-Policing
Identify the Cisco IOS commands required to configure and monitor percentage based CB-Policing
Explain how the two rate limits, average rate and peak rate, can be used to rate limit traffic
Identify the Cisco IOS commands required to configure and monitor CB-Shaping
Identify the Cisco IOS commands required to configure and monitor Frame Relay adaptive CB-Shaping on Frame Relay interfaces

Link Efficiency Mechanisms
Explain the various link efficiency mechanisms and their function
Identify the Cisco IOS commands required to configure and monitor CB header compression
Given a list of link speeds and a specific delay requirement, determine the proper fragment size to use at each link speed and identify the typical delay requirement for VoIP packets
Identify the Cisco IOS commands required to configure and monitor Multilink PPP with Interleaving
Identify the Cisco IOS commands required to configure and monitor FRF.12

QoS Best Practices
Explain the QoS requirements of the different application types
List typical enterprise traffic classes then identify the delay, jitter, packet loss and bandwidth requirements of each traffic class
Explain the best practice QoS implementations and configurations within the campus LAN
Explain the best practice QoS implementations and configurations on the WAN customer edge (CE) and provider edge (PE) routers

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 Explanation:

Source: Cisco IP QoS Introduction, Page 64

QUESTION 2
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 Incorrect:
B. No hop-by-hop signaling uses per-hop behavior

C. This is a feature of both models
Sources: Cisco IP QoS Introduction
http://www.cisco.com/en/US/tech/ CK5 43/ CK7 66/technologies_white_paper09186a00800a3e2f.shtml

QUESTION 3
The newly appointed Certkiller 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

Explanation:

Source: Cisco IP QoS Traffic Shaping and Policing

QUESTION 4
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 Explanation:

In the configuration example, CAR is applied on the input and output of a customer interface on the provider edge router. Traffic is policed to 256 Kbps on input and output, with some bursting allowed. All exceeding traffic is dropped at the provider edge.
The result of the configuration is that traffic to and from the customer is limited to the
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Recommended Training about 642-642 exam PDF
The following courses are the recommended training for 642-642 exam PDF.
642-642 Q & A with Explanations
642-642 Audio Exam
642-642 Study Guide
642-642 Preparation Lab

Exam Number/Code: 642-642
Exam Name: CCIP Quality of Service (QoS)

“CCIP Quality of Service (QoS)”, also known as 642-642 exam, is a Cisco certification.
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