300-420 Question 247
Select 3An enterprise network is experiencing poor voice call quality due to congestion in the WAN link. You have been tasked with designing an end-to-end QoS policy to address this issue. Which of the following configurations should you implement to ensure voice traffic is prioritized across the network?
- A
Mark voice traffic with DSCP EF (Expedited Forwarding) at the access layer.
- B
Apply a strict priority queue for voice traffic in the WAN link.
- C
Configure WRED (Weighted Random Early Detection) for voice traffic to prevent packet loss.
- D
Implement a bandwidth reservation policy for voice traffic using LLQ (Low Latency Queuing).
- E
Use a best-effort QoS model for voice traffic to avoid overcomplicating the configuration.
Show answer and explanation
Correct answers: A, B, D
Explanation
To ensure high-quality voice communication, an effective end-to-end QoS policy must prioritize voice traffic throughout the network. This involves marking the traffic with DSCP EF, configuring strict priority queuing for immediate forwarding, and reserving bandwidth using LLQ. These measures reduce latency, jitter, and packet loss, which are critical for voice traffic. WRED and best-effort models are not suitable for voice traffic, as they do not provide the necessary guarantees for high-quality performance.
- A. Correct.
Marking voice traffic with DSCP EF ensures it is tagged appropriately and recognized as high-priority traffic throughout the network.
- B. Correct.
Using a strict priority queue on the WAN link ensures that voice traffic is transmitted with the highest priority, reducing latency and jitter.
- C. Incorrect.
WRED is not suitable for voice traffic, as it introduces intentional packet drops, which can degrade voice quality. Voice traffic requires lossless handling.
- D. Correct.
LLQ guarantees a minimum amount of bandwidth for voice traffic, providing predictable performance and ensuring low latency.
- E. Incorrect.
A best-effort QoS model does not differentiate between traffic types, which fails to address the specific needs of voice traffic and can lead to poor call quality during congestion.