Troubleshooting Wireless IP Phone Connectivity Issue

A.

The issue described in the question involves two callers using the Cisco Unified Wireless IP Phone 7921 on the same access point (AP) running autonomous Cisco IOS Software. The problem occurs only when they call each other using the wireless IP phone, whereas the wired IP phone calls work correctly. The signaling and call routing appear to work correctly.

This type of issue is likely related to the quality of the wireless connection between the phone and the AP. There are several potential causes for this type of issue, including interference, congestion, or misconfiguration on the AP. The answers provided in the question suggest different configurations that could be causing the problem.

A. On the AP, DTIM is set to 2, Beacon Interval is set to 100, and PSPF is enabled. DTIM (Delivery Traffic Indication Message) is a mechanism used to indicate the presence of broadcast and multicast frames on a wireless network. A shorter DTIM interval may increase the frequency of beacon frames, which can result in better performance for voice traffic. However, setting a DTIM interval of 2 is not likely to cause this issue. The Beacon Interval is the time interval between beacons sent by the AP. A longer Beacon Interval may result in lower overhead, but may also result in slower performance. PSPF (Protected Port Service Function) is a security feature that isolates wireless client devices from each other. Enabling PSPF may prevent wireless clients from communicating with each other, which could cause the problem described in the question. However, the configuration settings provided in option A are not likely to be the cause of the problem.

B. On the AP, MFP is enabled for U-APSD, DHCP is not required, and PSPF is disabled. MFP (Management Frame Protection) is a security feature that protects management frames sent between the AP and wireless client devices. U-APSD (Unscheduled Automatic Power Save Delivery) is a power-saving mechanism used in voice applications. DHCP (Dynamic Host Configuration Protocol) is a protocol used to assign IP addresses to network devices. PSPF is a security feature that isolates wireless client devices from each other. Enabling MFP for U-APSD may improve security, but is not likely to cause the problem described in the question. DHCP is not likely to be related to the issue, since the wireless clients are able to connect to the network. PSPF is disabled, which means that wireless clients should be able to communicate with each other. Therefore, the configuration settings provided in option B are not likely to be the cause of the problem.

C. On the AP, WMM is enabled for U-APSD, DHCP is required, and PSK is enabled. WMM (Wi-Fi Multimedia) is a mechanism used to prioritize traffic on a wireless network. DHCP is a protocol used to assign IP addresses to network devices. PSK (Pre-Shared Key) is a type of authentication used in wireless networks. Enabling WMM for U-APSD may improve voice quality, but is not likely to cause the problem described in the question. DHCP is required for wireless clients to obtain IP addresses on the network. PSK should not affect the ability of wireless clients to communicate with each other. Therefore, the configuration settings provided in option C are not likely to be the cause of the problem.

D. On the AP, CAC is enabled for U-APSD, P2P-blocking is enabled, and Cisco CKM is enabled. CAC (Call Admission Control) is a mechanism used to manage the use of network resources for voice calls. U-APSD is a power-saving mechanism used in voice applications. P2P (Peer-to-Peer) blocking is a security feature that prevents wireless clients from communicating with each other. Cisco CKM (Client Key