350-401 Question 59
Select 3A network engineer is reviewing the QoS configuration for a hybrid wired and wireless network. On the wired side, priority queuing is configured for voice traffic using a class-map named 'VOICE'. On the wireless side, Wireless Multimedia (WMM) is enabled to prioritize voice traffic. However, users are reporting poor voice quality. What should the engineer verify to ensure end-to-end QoS is functioning correctly?
- A
Ensure the DSCP marking for voice traffic is preserved across wired and wireless boundaries.
- B
Verify that the 'VOICE' class-map is correctly assigned to the low-latency queue on the wired network.
- C
Confirm that WMM is properly enabled on all wireless access points.
- D
Check if the wired network's access layer switches are configured to trust CoS values from the wireless controllers.
- E
Ensure that the wireless SSID configuration includes a mapping of DSCP values to access categories (ACs).
Show answer and explanation
Correct answers: A, C, E
Explanation
End-to-end QoS requires consistent prioritization of traffic across the wired and wireless parts of the network. Preserving DSCP markings ensures that traffic is correctly classified. WMM must be enabled on all access points to provide wireless QoS, and mapping DSCP values to access categories ensures priority is maintained when moving between wired and wireless networks. While configuring low-latency queues and trusting CoS are important, they are secondary considerations in this scenario.
- A. Correct.
Preserving DSCP markings across wired and wireless boundaries is essential for maintaining QoS consistency end-to-end. Without this, traffic could lose its priority classification.
- B. Incorrect.
While assigning the 'VOICE' class-map to the low-latency queue is important, this alone doesn't address QoS issues if there are mismatches between wired and wireless QoS configurations.
- C. Correct.
WMM prioritization must be enabled on all access points to ensure wireless voice traffic is treated with the appropriate priority.
- D. Incorrect.
Trusting CoS values from the wireless controllers is not strictly necessary for end-to-end QoS, as DSCP markings are typically used for end-to-end QoS enforcement.
- E. Correct.
Mapping DSCP values to wireless access categories (ACs) ensures that traffic maintains its priority as it transitions from the wired network to the wireless domain.