CCNP Voice FAQ: Congestion Avoidance, Policing, Shaping, and Link Efficiency Mechanisms
Q1. Which of the following is not a tail drop flaw?
A. TCP synchronization
B. TCP starvation
C. TCP slow start
D. No differentiated drop
Q2. Which of the following statements is not true about RED?
A. RED randomly drops packets before the queue becomes full.
B. RED increases the drop rate as the average queue size increases.
C. RED has no per-flow intelligence.
D. RED is always useful, without dependency on flow (traffic) types.
Q3. Which of the following is not a main parameter of a RED profile?
A. Mark probability denominator
B. Average transmission rate
C. Maximum threshold
D. Minimum threshold
Q4. Which of the following is not true about WRED?
A. You cannot apply WRED to the same interface as CQ, PQ, and WFQ.
B. WRED treats non-IP traffic as precedence 0.
C. You normally use WRED in the core routers of a network.
D. You should apply WRED to the voice queue.
Q5. Which of the following is not true about traffic shaping?
A. It is applied in the outgoing direction only.
B. Shaping can re-mark excess packets.
C. Shaping buffers excess packets.
D. It supports interaction with Frame Relay congestion indication.
Q6. Which of the following is not true about traffic policing?
A. You apply it in the outgoing direction only.
B. It can re-mark excess traffic.
C. It can drop excess traffic.
D. You can apply it in the incoming direction.
Q7. Which command is used for traffic policing in a class within a policy map?
Q8. Which of the following does not apply to class-based shaping?
A. It does not support FRF.12.
B. It classifies per DLCI or subinterface.
C. It understands FECN and BECN.
D. It is supported via MQC
Q9. Which of the following is not a valid statement about compression?
A. Many compression techniques remove as much redundancy in data as possible.
B. A single algorithm might yield different compression ratios for different data types.
C. If available, compression is always recommended.
D. Compression can be hardware based, hardware assisted, or software based.
Q10. Which of the following is not true about Layer 2 payload compression?
A. It reduces the size of the frame payload.
B. It reduces serialization delay.
C. Software-based compression might yield better throughput than hardware-based compression.
D. Layer 2 payload compression is recommended on all WAN links.
Q11. Which of the following is the only true statement about header compression?
A. RTP header compression is not a type of header compression.
B. Header compression compresses the header and payload.
C. Header compression may be class based.
D. Header compression is performed on a session-by-session (end-to-end) basis.
Q12. Which of the following is not true about fragmentation and interleaving?
A. Fragmentation and interleaving is recommended when small delay-sensitive packets are present.
B. Fragmentation result is not dependent on interleaving.
C. Fragmentation and interleaving might be necessary, even if LLQ is configured on the interface.
D. Fragmentation and interleaving is recommended on slow WAN links.
Q13. Name two of the limitations and drawbacks of tail drop.
Q14. Explain TCP global synchronization.
Q15. Explain TCP starvation.
Q16. Explain why RED does not cause TCP global synchronization.
Q17. What are the three configuration parameters for RED?
probability denominator (MPD). While the size of the queue is smaller than the minimum threshold, RED does not drop packets. As the queue size grows, so does the rate of packet drops. When the size of the queue becomes larger than the maximum threshold, all arriving packets are dropped (tail drop behavior). The mark probability denominator is an integer that dictates to RED to drop one of MPD (as many packets as the value of mark probability denominator); the size of the queue is between the values of minimum and maximum thresholds.
Q18. Briefly explain how WRED is different from RED.
Q19. Explain how class-based weighted random early detection is implemented.
Q20. Explain how assured forwarding per-hop behavior is implemented on Cisco routers.
Q21. List at least two of the main purposes of traffic policing.
Q22. List at least two of the main purposes of traffic shaping.
Q23. List at least four of the similarities and differences between traffic shaping and policing.
Answer: The similarities and differences between traffic shaping and policing include the following:
- Both traffic shaping and traffic policing measure traffic. (Sometimes, different traffic classes are measured separately.)
- Policing can be applied to the inbound and outbound traffic (with respect to an interface), but traffic shaping applies only to outbound traffic.
- Shaping buffers excess traffic and sends it according to a preconfigured rate, whereas policing drops or re-marks excess traffic.
- Shaping requires memory for buffering excess traffic, which creates variable delay and jitter; policing does not require extra memory, and it does not impose variable delay.
- Policing can re-mark traffic, but traffic shaping does not re-mark traffic.
- Traffic shaping can be configured to shape traffic based on network conditions and signals, but policing does not respond to network conditions and signals.
Q24. In the token bucket scheme, how many tokens are needed for each byte of data to be transmitted?
Q25. Explain in the single bucket, single rate model when conform action and exceed action take place.
Q26. What is the formula showing the relationship between CIR,Bc, and Tc?
CIR (bits per second) = Bc (bits) / Tc (seconds)
Q27. Compare and contrast Frame Relay traffic shaping and class-based traffic shaping.
Q28. Briefly explain compression.
Q29. Briefly explain Layer 2 payload compression.
Q30. Provide a brief explanation for header compression.
Q31. Is it possible to mitigate the delay imposed by the large data units ahead of delay-sensitive packets in the hardware (Tx) queue?
Q32. Where should link efficiency mechanisms be applied?