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

642-642 QOS
Quality of Service Exam

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

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* 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.
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With the complete collection of questions and answers, 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

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

1.What is the purpose of the qos pre-classify command?
A. to enable the IOS to copy the ToS field from the original IP header to the outer tunnel IP header
B. to enable the IOS to copy the ToS field from the outer tunnel IP header back into the original IP header
C. to enable the IOS to classify the packet based on the original IP header instead of the tunnel IP
header
D. to enable the IOS to classify the packet based on the outer tunnel IP header instead of the
original IP header
E. to enable class-based marking on tunnel interface
F. to enable class-based marking on IPSec crypto maps

Answer:C

2.What are two benefits of WFQ? (Choose two.)
A. WFQ is very easy to configure, and no manual traffic classification is necessary.
B. WFQ can provide fixed-bandwidth and fixed-delay guarantees.
C. WFQ can provide fixed-bandwidth guarantees.
D. WFQ can provide fixed-delay guarantees.
E. WFQ prevents the large-volume flows with large packet size from starving out the low-volume
flows with small packet size.
F. Based on DSCP, WFQ allows weighted, random dropping of packets when the WFQ system is
full.

Answer:AE

5.Which technology is required when configuring FRF.12 on a Cisco device?
A. FRF11.c
B. FRF.8
C. VoFR
D. MLP with interleaving
E. FRTS
F. WRED

Answer:E

6.What are three methods of reducing delay for critical applications in a converged network?
(Choose three.)
A. Apply payload compression.
B. Increase link capacities.
C. Apply header compression.
D. Increase LFI fragment size.
E. Reduce inter-packet gaps.
F. Increase all queue depths.

Answer:ABC
7.At the network layer, IP packets are typically classified based on which three items? (Choose
three.)
A. packet length
B. VLAN Identifier
C. flow control bits
D. source and destination IP addresses
E. content of the ToS byte

Answer:ADE

8.What are three reasons link efficiency mechanisms are deployed on WAN links? (Choose three.)
A. decrease delay
B. decrease jitter
C. increase link speed
D. increase throughput
E. decrease propagation delay

Answer:ABD

9.Which mechanism is used for the prioritizing, protection, and isolation of traffic based on
marking?
A. classification and marking
B. congestion management
C. congestion avoidance
D. metering
E. policing
F. shaping
Answer:B

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