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IP Communications Quality of Service (QoS) : 642-642 Exam

Exam Number/Code: 642-642
Exam Name: IP Communications Quality of Service (QoS)
VUE Code: 642-642
Questions Type: Single choice,
Real Exam Question Numbers: 45-55 questions
Exam Language(s): English

Exam Description Introduction
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

“IP Communications Quality of Service (QoS)”, also known as 642-642 exam, is a Cisco certification.
Preparing for the 642-642 exam Searching 642-642 Test Questions, 642-642 Exam, 642-642 Dumps

With the complete collection of questions and answers Q&as with Expert Explanations, Pass4sure has assembled to take you through 90 Q&As to your 642-642 Exam preparation. In the 642-642 exam resources, you will cover every field and category in IP Communications helping to ready you for your successful Cisco Certification.

QUESTION 16:
Auto QoS is which type of Cisco IOS command?
A. interface
B. global
C. policy-map
D. service-map
E. serial interface only
Answer: A
Explanation:
To install the quality-of-service (QoS) class maps and policy maps created by the
AutoQoS for the Enterprise feature, use the auto qos command in interface configuration
mode. To remove the QoS policies, use the no form of this command.
Reference:

http://www.cisco.com/en/US/products/sw/iosswrel/ps5207/products_command_reference_chapter09186a00801

a
QUESTION 17:
Which two components are associated with the DiffServ model? (Choose two.)
A. hop-by-hop signaling
B. per-hop behavior
C. RSVP
D. Hard QoS
E. DSCP use of class selector
Answer: B, E
Explanation:
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The Differentiated Services (DiffServ) model describes services associated with traffic
classes. Traffic classes are identified by the value of the DiffServ Code Point (DSCP
replaces IP precedence in the ToS field of the IP header).
The main goal of the DiffServ model are to provide scalability and a similar level of QoS
to the Int Serv model, without having to do it on a per-flow basis. The network simply
identifies a class (not application) and applies the appropriate per-hop behavior (QoS
mechanism)
Reference: Introduction to IP QoS (Course) p.34
Not A: DiffServ does not have signaling
QUESTION 18:
What is true about a DSCP marked packet when it reaches an IP precedence based
device?
A. The eight DSCP bits are all set to zero.
B. The last three bits of the DSCP are set to 101.
C. The 8 DSCP AF classes will be mapped into the 8 levels of IP precedence.
D. Bits 7-5 of DSCP have the same position and meaning as IP precedence.
Answer: D
Reference: Cisco Press – DQOS Exam Certification Guide p.120
QUESTION 19:
SIMULATION
Simulation Exhibit:
You are working as a network administrator at PassGuide .com. You are required to
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configure the PassGuide 1 WAN edge router: you must configure the appropriate
MQC based queuing mechanism for the outbound traffic to the WAN (S0/0) so that
the following bandwidth requirements will be met. A strict priority queue with a
168 Kbps bandwidth guarantee for the class voice is reserved, a minimum
bandwidth guarantee of 30 Kbps is configured for the class interactive, a minimum
bandwidth guarantee of 16 Kbps for class bulk, and the default class is configured
for WFQ with no bandwidth guarantee.
In addition, also limit the bulk traffic class to an average rate of 24 Kbps by
buffering excess traffic (use the IOS default Bc and Be).
In addition, also limit the bulk traffic class to an average rate of 24 Kbps by
buffering excess traffic (use the IOS default Bc and Be).
* Use a policy-map called “IIq-policy” and reference the existing class-maps
already configured on the PassGuide 1 router.
Traffic Class Name Bandwidth Guarantee
voice 168 Kbps maximum (use the IOS default burst value)
interactive 30 Kbps minimum
bulk 16 Kbps minimum (For the bulk traffic class, also limit the traffic to an average rate
of 24 Kbps by buffering excess traffic (use the IOS default Bc and Be))
class-default Weighted Fair Queue with no bandwidth guarantee
Simulation Output exhibit #1:
Simulation Output exhibit #2:
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Answer:
PassGuide 1(config)#policy-map llq-policy
PassGuide 1(config-pmap)#class voice
PassGuide 1(config-pmap-c)#priority 168
PassGuide 1(config-pmap-c)#class interactive
PassGuide 1(config-pmap-c)#bandwidth 30
PassGuide 1(config-pmap-c)#class bulk
PassGuide 1(config-pmap-c)#bandwidth 16
PassGuide 1(config-pmap-c)#shape average 2400
PassGuide 1(config-pmap-c)#class class-default
PassGuide 1(config-pmap-c)#fair-queue
PassGuide 1(config-pmap-c)#interface serial 0/0
PassGuide 1(config-if)#service-policy output llq-policy
PassGuide 1(config-if)#end
PassGuide 1#copy running-config startup-config
Explanation:
policy-map llq-policy (Not: iiq-policy)
shape average 24000 (not shape peak 24(shape in bps not kbps) and shape to average not
peak)
Note: Uncertainty:
Actual exam problems:
1. Unable to use the command: fair-queue
Note: There is no need to use the ip nbar protocol-discovery command as the question
doesn’t state to configure NBAR.
QUESTION 20:
Command exhibit: mis qos trust pass-through dscp
Your apprentice PassGuide is configuring a Catalyst 2950 Switch. What is the
purpose of the command she is submitting (see exhibit)?
A. The command configures a port to trust the incoming CoS and not modify the
incoming DSCP when sending the frame out.
B. The command configures a port to trust the incoming CoS and to generate the internal
DSCP based on the incoming CoS. The internalr DSCP will then determine the gress
DSCP.
C. The command configures a port to trust the incoming CoS and DSCP values.
D. The command configures a port to trust the incoming CoS and to generate the internal
DSCP based on the incoming DSCP. The internal DSCP will then determine the egress
DSCP.
E. The command configures a port to trust the incoming CoS and bypass the
CoS-to-DSCP maps for generating the internal DSCP.
F. The command configures a port to trust the incoming CoS and bypass the
DSCP-to-CoS maps for generating the egress CoS.
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Answer: A