WiFi Capacity, Roaming and Performance Troubleshooting Playbook

Coverage and capacity are not the same

A room can have excellent RSSI and still perform poorly when too many active clients share the same airtime, when interference is high, or when the AP uplink is constrained.

Roaming is a client decision

The network can provide mechanisms and information that assist roaming, but the client ultimately decides when to move between APs. Test the actual client families that matter to the project, especially phones, scanners and voice devices.

Capacity questions

• How many simultaneously active clients exist in the cell?
• What applications dominate airtime?
• What channel width is configured?
• How much channel utilisation exists during busy time?
• Are retries high?
• Are clients stuck on older bands or data rates?
• Does the AP uplink negotiate at the expected Ethernet speed?

Transmit power symmetry

Cisco's site-survey guidance explicitly warns that an AP can transmit more strongly than client devices. The survey may show downlink coverage where the return path remains weak. Power design therefore needs to consider the client, not just the AP.

Field troubleshooting sequence

1. Identify the client, AP, band, channel and channel width.
2. Record RSSI and SNR.
3. Check retries and channel utilisation.
4. Run a local LAN throughput test before blaming Internet bandwidth.
5. Check AP Ethernet link speed/errors and PoE state.
6. Compare with another client at the same position.
7. Move through the expected roam path and record when the client changes AP.

What works

• Busy-hour measurements.
• Representative client devices.
• Post-install validation after automatic RF algorithms settle.
• Separating RF performance from WAN performance.

What does not work

• Running one speed test beside the AP and declaring the WLAN good.
• Assuming full signal bars mean low contention.
• Adding APs without checking co-channel interference.