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CCNP Voice FAQ: IP Quality of Service

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CCNP Voice FAQ: IP Quality of Service

Q1. Which of the following items is not considered one of four major issues and challenges facing converged enterprise networks?
A. Available bandwidth
B. End-to-end delay
C. Delay variation (jitter)
D. Packet size

Answer: D

Q2. Which of the following is defined as the maximum bandwidth of a path?
A. The bandwidth of the link within the path that has the largest bandwidth
B. The bandwidth of the link within the path that has the smallest bandwidth
C. The total of all link bandwidths within the path
D. The average of all the link bandwidths within the path

Answer: B

Q3. Which of the following is not considered one of the main methods to tackle the bandwidth availability problem?
A. Increase (upgrade) the link bandwidth.
B. Classify and mark traffic and deploy proper queuing mechanisms.
C. Forward large packets first.
D. Use compression techniques.

Answer: C

Q4. Which of the following is not considered a major delay type?
A. Queuing delay
B. CEF (Cisco Express Forwarding) delay
C. Serialization delay
D. Propagation delay

Answer: B

Q5. Which of the following does not reduce delay for delay-sensitive application traffic?
A. Increasing (upgrade) the link bandwidth
B. Prioritizing delay-sensitive packets and forwarding important packets first
C. Layer 2 payload encryption
D. Header compression

Answer: C

Q6. Which of the following approaches does not tackle packet loss?
A. Increase (upgrade) the link bandwidth.
B. Increase the buffer space.
C. Provide guaranteed bandwidth.
D. Eliminate congestion avoidance.

Answer: D

Q7. Which of the following is not a major step in implementing QoS?
A. Apply access lists to all interfaces that process sensitive traffic
B. Identify traffic types and their requirements
C. Classify traffic based on the requirements identified
D. Define policies for each traffic class

Answer: A

Q8. Which of following is not one of the three main QoS models?
A. MPLS QoS
B. Differentiated services
C. Best effort
D. Integrated services

Answer: A

Q9. Which two of the following items are considered drawbacks of the best-effort model?
A. Inability to scale
B. Lack of service guarantee
C. Lack of service differentiation
D. Difficulty in implementing (complexity)

Answer: B and C

Q10. Which of the following is not a function that IntServ requires to be implemented on the routers along the traffic path?
A. Admission control and policing
B. Classification
C. Queuing and scheduling
D. Fast switching

Answer: D

Q11. Which of the following is the role of RSVP within the IntServ model?
A. Routing
B. Switching
C. Signaling/Bandwidth Reservation
D. Caching

Answer: C

Q12. Which of the following is not considered a benefit of the IntServ model?
A. Explicit end-to-end resource admission control
B. Continuous signaling per active flow
C. Per-request policy admission control
D. Signaling of dynamic port numbers

Answer: B

Q13. Which of the following is not true about the DiffServ model?
A. Within the DiffServ model, QoS policies (are deployed to) enforce differentiated treatment of the defined traffic classes.

B. Within the DiffServ model, classes of traffic and the policies are defined based on business requirements; you choose the service level for each traffic class.

C. Pure DiffServ makes extensive use of signaling; therefore, it is called hard QoS.

D. DiffServ is a scalable model.

Answer: C

Q14. Which of the following is not a QoS implementation method?
A. Cisco IOS CLI
B. MQC
C. Cisco AVVID (VoIP and Enterprise)
D. Cisco SDM QoS Wizard

Answer: C

Q15. Which of the following is not a major step in implementing QoS with MQC?
A. Define traffic classes using the class map.

B. Define QoS policies for the defined traffic classes using the policy map.

C. Apply the defined policies to each intended interface using the service-policy command.

D. Enable AutoQoS.

Answer: D

Q16. Which of the following is the simplest QoS implementation method with an option specifically for VoIP?
A. AutoQoS (VoIP)
B. CLI
C. MQC
D. Cisco SDM QoS Wizard

Answer: A

Q17. Select the most time-consuming and the least time-consuming QoS implementation methods.
A. CLI
B. MQC
C. AutoQoS
D. Cisco SDM QoS Wizard

Answer: A and C
CLI is the most time-consuming QoS implementation method, and AutoQoS is the least timeconsuming QoS implementation method.

Q18. What is the most significant advantage of MQC over CLI?
A. It requires little time to implement.
B. It requires little expertise to implement.
C. It has a GUI and interactive wizard.
D. It separates traffic classification from policy definition.

Answer: D

Q19. Before you enable AutoQoS on an interface, which two of the following must you ensure have been configured on that interface?
A. Cisco modular QoS is configured.
B. CEF is enabled.
C. The SDM has been enabled.
D. The correct bandwidth on the interface is configured.

Answer: B and D

Q20. Select the item that is not a main service obtained from SDM QoS.
A. It enables you to implement QoS on the network.
B. It enables you to fine-tune QoS on the network.
C. It enables you to monitor QoS on the network.
D. It enables you to troubleshoot QoS on the network.

Answer: B

Q21. List the four key quality issues with converged networks.

Answer: The four key quality issues with converged networks include available bandwidth, end-to-end delay, variation of delay (jitter), and packet loss.

Q22. Provide a definition for maximum available bandwidth and average available bandwidth per flow.

Answer: The maximum available bandwidth is equal to the bandwidth of the lowest link (from source to destination). The average bandwidth available per flow is the maximum available bandwidth divided by the number of flows.

Q23. List at least three types of delay.

Answer: Delay types include processing delay, queuing delay, serialization delay, propagation delay,
compression/decompression delay, and encryption/decryption delay.

Q24. Provide at least three ways to reduce delay.

Answer: You can reduce delay by increasing the link bandwidth (capacity), prioritizing delay-sensitive packets, reprioritizing packets if necessary, performing payload compression, or performing header compression.

Q25. Provide at least two ways to reduce or prevent loss of important packets.

Answer: You can reduce or prevent loss of important packets by doing any of the following:

  • Increasing the (upgrade) link bandwidth (capacity)
  • Guaranteeing enough bandwidth to drop sensitive (important) packets
  • Preventing congestion by dropping less important packets before congestion occurs

Q26. Provide a definition for QoS.

Answer: The latest definition included in Cisco educational material defines QoS as the ability of the network to provide better or “special” service to a set of users or applications or both to the detriment of other users or applications or both.

Q27. List the three key steps in implementing QoS on a network.

Answer: The three key steps involved in implementing QoS on a network include the following:

  1. Identifying the network traffic and its requirements
  2. Defining traffic classes
  3. Defining a QoS policy for each traffic class

Q28. List the three main QoS models.

Answer: The three main QoS models are best-effort, IntServ, and DiffServ.

Q29. Provide a short description of the best-effort model.

Answer: The best-effort model is the default; it does not differentiate among different traffic types.

Q30. What are the benefits and drawbacks of the best-effort model?

Answer: The benefits of the best-effort model are that it is scalable, and it requires special mechanisms.
The drawbacks of the best-effort model are that it does not provide service guarantee, and it does not provide Differentiated Service.

Q31. Provide a short description for the IntServ model.

Answer: IntServ is a guaranteed QoS model that is often referred to as Hard QoS. It uses a signaling
mechanism such as RSVP to make resource reservation and guarantee for each traffic flow before it becomes active. If resources are secured first, the flow is not admitted. IntServ can provide multiple service levels and uses intelligent queuing mechanisms to provide guaranteed rate and controlled load.

Q32. Name the functions that the IntServ model requires on the network routers and switches.

Answer: The IntServ model requires the following functions on the network routers and switches:

  • Admission control
  • Classification
  • Policing
  • Queuing
  • Scheduling

Q33. What are the benefits and drawbacks of the IntServ model?

Answer: The benefits of the IntServ model include explicit end-to-end resource admission control, perrequest policy admission control, and signaling of dynamic port numbers. The drawbacks of the IntServ model include continuous signaling because of stateful architecture and low scalability because of the flow-based nature of the model.

Q34. What are the main features of the DiffServ model?

Answer: The DiffServ model was designed to overcome the limitations of the best-effort and the IntServ models. Within this model, the network traffic is classified and marked, differentiated treatment of traffic classes is enforced by network QoS policies, and different service levels are chosen for traffic classes based on business requirements.

Q35. What are the benefits and drawbacks of the DiffServ model?

Answer: The benefits of the DiffServ model include high scalability and the ability to provide many different service quality levels.
The drawbacks of the DiffServ model include lack of an absolute service guarantee and a requirement for implementation of complex mechanisms throughout the network.

Q36. What are the four QoS implementation methods?

Answer: The four QoS implementation methods are as follows:

  • Legacy command-line interface (CLI) for basic QoS deployments
  • Modular QoS command-line interface (MQC) for high-level deployment and fine-tuning of QoS
  • AutoQoS for automatic (general) QoS configuration
  • Cisco Router and Security Device Manager (SDM) QoS Wizard for web-based (GUI) and interactive QoS configuration

Q37. Which of the four QoS implementation methods is nonmodular and the most time consuming?

Answer: Of the four QoS implementation methods, legacy CLI is nonmodular and the most time consuming.

Q38. What are the main benefits of MQC?

Answer: Modular QoS command-line interface (MQC) allows implementation of the most recent and
modern QoS features and mechanisms in a modular fashion. It separates the concept and process of traffic classification from the definition and deployment of QoS policy. MQC is less error prone and promotes code reuse and consistency.

Q39. What is the most important advantage of AutoQoS?

Answer: The main advantage of AutoQoS is that it simplifies the task of QoS configuration. Network administrators who lack in-depth knowledge of QoS commands and features can use AutoQoS to implement those features consistently and accurately.

Q40. What are the prerequisites for Auto QoS VoIP?

Answer: Enabling CEF and configuring the correct bandwidth on the interface are the prerequisites for Auto QoS VoIP.

Q41. What are the prerequisites for Auto QoS for the enterprise?

Answer: Enabling CEF and NBAR, plus configuring the correct bandwidth on the interface, are the prerequisites for Auto QoS on the enterprise.

Q42. Which of the four QoS implementation methods is the fastest?

Answer: AutoQoS is the fastest QoS implementation method.

Q43. What are the three main tasks that you can accomplish using the SDM QoS Wizard?

Answer: The SDM QoS Wizard enables you to do three things:

  • Implement QoS
  • Monitor QoS
  • Troubleshoot QoS on the network