Learn About Optimizing Converged Cisco Networks

The following questions are from the MeasureUp Practice Test for Cisco’s exam 642-845: Optimizing Converged Cisco Networks (ONT). This exam is one of the requirements for the Cisco Certified Network Professional (CCNP) certification.

The audience for this exam includes individuals who are responsible for optimizing network performance and implementing quality of service (QoS) for converged networks. Experience with implementing QoS and Voice over IP (VoIP) networks will help you prepare for this exam.

Objective: Describe Cisco VoIP implementations.
Sub-objective: Describe and identify basic voice components in an enterprise network (e.g., gatekeepers, gateways, etc.).

Single answer, multiple-choice

Which statement correctly specifies the characteristics of TCP, UDP and RTP with respect to reliability, reordering and time-stamping?

A.    UDP does not provide reliability and reordering, but it does provide time-stamping.
B.    RTP does not provide reliability, but it does provide reordering and time-stamping.
C.    TCP provides reliability, reordering and time-stamping.
D.    RTP provides reliability, reordering and time-stamping.

Answer:
B

Tutorial:
Realtime Transport Protocol (RTP) provides sequence numbering (reordering) and time-stamping, but it does not offer reliability. The reliability feature of TCP is not suitable for voice applications. Therefore, RTP is used to transport digital voice in packet telephony networks.

User Datagram Protocol (UDP) provides no reliability, no sequence numbering (reordering) and no time-stamping. Lack of the latter two features makes UDP unsuitable for transporting voice.

TCP provides reliability and sequence numbering but not time-stamping. Time-stamping is a feature required for transporting voice. The acknowledgement and segment resending features of TCP make it a reliable transport protocol but too slow for voice transport. Also, the reliability feature of retransmitting lost data is not useful for voice applications.

References:
Explaining Protocols Used in Voice Encapsulation
Optimizing Converged Cisco Networks
Module 2

Protocols Used in Voice Encapsulation
CCNP ONT: Official Exam Certification Guide
Chapter 1

Objective: Describe QoS considerations.
Sub-objective: Describe strategies for QoS implementations (e.g., QoS policy, QoS models, etc.).

Multiple answer, multiple-choice

Which statements apply to the policy-map command? (Choose all that apply.)

A.    It specifies where the policy will be implemented.
B.    It specifies what will be done to the traffic.
C.    It contains a case-sensitive name and one or more traffic classes, each of which may have a QoS policy applied to it.
D.    It contains three main elements: a case-sensitive name, one or more match statements and an instruction on how to evaluate multiple match statements.
E.    It specifies what traffic you care about.

Answer:
B, C

Tutorial:
A policy-map command contains a case-sensitive name and one or more traffic classes, each of which may have a QoS policy applied to it. Up to 256 traffic classes can be associated with a single-traffic policy. Multiple policy-maps can be nested to influence the sequence of QoS actions. A policy-map defines what will be done to the traffic.

The service-policy command specifies where a policy (policy-map) is applied.

Each traffic class is defined using a class-map. A class-map command contains three main elements: a case-sensitive name, one or more match statements and an instruction on how to evaluate multiple match statements. A class-map can be configured in one of two modes: match all, meaning all conditions must be satisfied and match any, meaning that one condition satisfied is enough. Match all is the default mode for class-maps. The class-map command defines what traffic you care about.

References:
Identifying Models for Implementing QoS: Modular QoS CLI Components
Optimizing Converged Cisco Networks, Module 3

QoS Implementation Methods: Modular QoS Command Line Interface
CCNP ONT: Official Exam Certification Guide, Chapter 2

Applying QoS Features Using the MQC, Cisco.com, http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/qos_mqc.html
 

Objective: Describe DiffServ QoS implementations.
Sub-objective: Describe classification and marking (e.g., CoS, ToS, IP precedence, DSCP, etc.).

Single answer, multiple-choice

Which of the following is a marking field (also called a marker)?

A.    ECN
B.    MPLS
C.    802.1Q
D.    CoS or PRI

Answer:
D

Tutorial:
The priority field on the ISL and 802.1Q/P frames is referred as the class of service (CoS) field. CoS is one of the main link layer markers (marking fields). Other examples of link layer markers are DE on Frame Relay and EXP on Multiprotocol Label Switching (MPLS).

The least important two bits in the Type of Service (ToS) byte in an IP packet are the Explicit Congestion Notification (ECN) bits. The six most important bits of the ToS byte are the Differentiated Services Code Point (DSCP) bits. DSCP bits are marker bits used for QoS, but the ECN bits are used for flow-control purposes.

MPLS is the acronym for Multiprotocol Label Switching. On MPLS packets, the EXP field is used for marking.

The IEEE 802.1Q standard defines a 4-byte header that is added to the Ethernet frame header after the source MAC address field. 802.1Q is used as a trunking mechanism between Ethernet LAN devices. The priority or CoS field is used for marking in the 802.1Q header.

References:

Introducing Classification and Marking: Marking,
Optimizing Converged Cisco Networks, Module 4

Classification and Marking, CCNP ONT: Official Exam Certification Guide, Chapter 3

Marking Network Traffic, Cisco.com, http://www.cisco.com/en/US/docs/ios/qos/configuration/guide/mrkg_netwk_traffic.html

Objective: Implement AutoQoS.
Sub-objective: Explain the functions and operations of AutoQoS.

Multiple answer, multiple-choice

Which statements correctly describe AutoQoS? (Choose all that apply.)

A.    AutoQoS provides QoS provisioning for routers and switches.
B.    AutoQoS requires a license that can be costly.
C.    Configuring AutoQoS can be complex because it requires Modular Quality of Service (QoS) Command-Line Interface (CLI) (MQC) knowledge.
D.    AutoQoS helps in reducing configuration errors.
E.    Configuring AutoQoS can take a significant amount of time.

Answer:
A, D

Tutorial:
Deploying QoS using AutoQoS is simple and quick. By using AutoQoS, enterprises can reduce configuration errors and costs. AutoQoS is an IOS feature and requires no license.

References:
Implement Cisco AutoQoS: Automating the Delivery of Network QoS,
Optimizing Converged Cisco Networks, Module 5

Implementing AutoQoS: Introducing AutoQoS,
CCNP ONT: Official Exam Certification Guide, Chapter 7

Automation for Quality of Service Deployments: Cisco AutoQoS,
Cisco.com, http://www.cisco.com/en/US/technologies/tk543/tk879/technologies_white_paper0900aecd803228e0.html

Objective: Implement WLAN security and management.
Sub-objective: Describe and configure WLAN QoS.

Multiple answer, multiple-choice

In the Split-MAC architecture, which of the following are considered non-real-time functions handled by the wireless LAN controller? (Choose two.)

A.    Beacon generation.
B.    Frame translation and bridging functions.
C.    Probe response.
D.    MAC layer encryption.
E.    System-wide policies for user mobility, QoS and security.

Answer:
B, E

Tutorial:
In the Split-MAC architecture, processing of 802.11 data and management protocols and access point capabilities are distributed between a lightweight access-point (LWAP) and a centralized wireless LAN controller (WLC).

Time-sensitive and real-time functions, such as beacon generation, probe response and MAC layer encryption, are handled in the LWAP.

Non-real-time functions, such as 802.11 management protocol, frame translation and bridging functions, plus system-wide policies for user mobility, QoS and security, are handled by the WLC.

References:
Implementing WLAN QoS: Lightweight Access Point – Split MAC Architecture
Optimizing Converged Cisco Networks, Module 6

Wireless LAN QoS Implementation: Split MAC Architecture and Lightweight Access Point,
CCNP ONT: Official Exam Certification Guide, Chapter 8

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