Packet drops and jitter can greatly reduce the quality of a Voice Over WiFi call. When troubleshooting Voice Over WiFi call quality issues the following items should be looked at.
• QoS Configuration
• Signal Strength
• Packet Loss
A simple ping test can be used to exam the latency. The latency should not exceed 150ms, ideally it should be much less. Also, the latency should be consistent; as to not introduce jitter or variance in the latency (jitter should be less than 30ms).
You should also validate signal strength, which should be -67dBm or stronger; and you should have an SNR higher than 25dBm. Last, but not least packet loss should be less than 1%.
A WiFi network analyzer like the EtherScope® nXG Portable Network Expert can be used to greatly reduce the amount of time troubleshooting such issues. For example, a WiFi Analysis test can be used to gather all the stats along with ping times from the two end points in one simple test.