300-365 · Question #108
An engineer has found that voice traffic on the WLAN with ID 338789750 is being sent at best effort from a client that is experiencing issues despite having QoS and CAC enabled. Which option causes…
The correct answer is B. The client does not support TSPEC. When a wireless client does not support TSPEC (Traffic Specification), it cannot request admission through Call Admission Control (CAC), so its voice traffic is sent at best effort instead of the voice access category.
Question
An engineer has found that voice traffic on the WLAN with ID 338789750 is being sent at best effort from a client that is experiencing issues despite having QoS and CAC enabled. Which option causes the traffic to be sent at best effort?
Options
- AThe QoS profile for Platinum has been left at default settings.
- BThe client does not support TSPEC.
- CWMM is configured as required.
- Dmsl qos trust cos is not required on the switchport.
How the community answered
(45 responses)- A4% (2)
- B80% (36)
- C11% (5)
- D4% (2)
Why each option
When a wireless client does not support TSPEC (Traffic Specification), it cannot request admission through Call Admission Control (CAC), so its voice traffic is sent at best effort instead of the voice access category.
The Platinum QoS profile maps DSCP values to AC_VO by default; leaving it at default would still prioritize voice, not downgrade it to best effort.
WMM CAC requires a client to send a TSPEC request to the AP to reserve bandwidth for voice or video traffic. If the client does not support TSPEC, it cannot negotiate admission to the voice access category (AC_VO), and the AP has no mechanism to grant or deny the request - causing the client to transmit voice traffic at the default best-effort (AC_BE) queue despite QoS and CAC being enabled on the WLAN.
Configuring WMM as required means non-WMM clients are rejected; clients that associate have WMM capability and this setting alone would not force voice to best effort.
The msl qos trust cos command applies to wired switchport QoS trust and has no direct effect on how a wireless client classifies its uplink traffic toward the AP.
Concept tested: WMM CAC and TSPEC client admission control
Source: https://www.cisco.com/c/en/us/td/docs/wireless/controller/8-10/config-guide/b_cg810/wlan_qos.html
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