An ACME company employee complained about a recent poor-quality VoIP call while moving around their office environment HPE Aruba Networking Central reported a fair UCC score for this call while your VoIP engineer reported that their systems reported a MOS of 2, 3. The VoIP devices are operating over the 5GHz frequency band. What are the possible contributing factors? (Select two.)

The scenario describes poor VoIP quality (MOS of 2.3) for a mobile user on the 5GHz band. The user's movement is a key factor, pointing towards issues with roaming or localized environmental problems.
1. Insufficient Cell Overlap (A): Wi-Fi deployments designed for basic data coverage often lack the sufficient cell overlap (recommended -67 dBm signal at cell edge for voice) required for seamless roaming. As the user moves, they can experience delays or packet loss during the handoff between APs, causing audio gaps and a low MOS score.
2. Localized Interference (C): The user could have moved through an area with significant non-Wi-Fi interference on the 5GHz band (e.g., from wireless video cameras, radar, or cordless phones). This interference would corrupt packets, increasing retransmissions and jitter, which severely degrades real-time voice quality.

B. 802.11r (Fast BSS Transition) is a standard specifically designed to speed up roaming and improve the performance of applications like VoIP.
D. While disabling 802.11k would negatively impact roaming efficiency, insufficient cell overlap (A) is a more fundamental RF design flaw that causes similar, if not more severe, roaming problems.
E. Zigbee devices operate in the 2.4GHz ISM band. The question explicitly states the VoIP devices were operating on the 5GHz band, so Zigbee is not a relevant source of interference.

1. Aruba Voice over Wi-Fi (VoFi) and Aruba Wi-Fi Validated Reference Design Guide, (April 2020).

For Answer A: Page 8, under the "RF Design" section, states, "For voice, the recommended cell edge is –67 dBm. This provides sufficient overlap for seamless roaming..." A deployment focused only on coverage might not meet this requirement.

For Answer C: Page 10, in the "Interference" section, notes, "Sources of interference in the 5 GHz band include... cordless phones, wireless video cameras, and radar." This confirms that localized 5GHz interference is a valid concern.

For Answer B & D: Page 11, under "802.11r, 802.11k, and 802.11v," the guide states, "Aruba recommends enabling 802.11k, 802.11v, and 802.11r on voice SSIDs," confirming that enabling these features is a best practice, and disabling them would be detrimental.

2. Aruba Mobility Fundamentals, Rev 20.11, Student Guide, (2020).

For Answer E: Module 2, "RF Fundamentals," discusses sources of interference, consistently placing Zigbee as a 2.4GHz interferer, distinct from the 5GHz band where the issue occurred.