Campus Wireless Network Design
RF first, then APs
Wireless design starts with a site survey - predictive (modeling), passive (listen), or active (validate) - and a stated coverage and capacity requirement. Coverage designs target signal strength (commonly around -67 dBm RSSI for voice/data at the cell edge); capacity designs target client density and per-client throughput. Know channel planning (2.4 GHz has 3 non-overlapping channels; 5 GHz has many more), channel width (20/40/80 MHz trade range for throughput), and co-channel interference versus adjacent-channel interference.
Architecture and roaming
Understand controller-based versus controller-less/cloud architectures, CAPWAP tunnels, and local versus centralized data forwarding. Roaming types: L2 roaming (same subnet) versus L3 roaming (different subnet, requires mobility tunneling or an anchor). Fast roaming (802.11r) matters for voice. Also know band steering, airtime fairness, and WPA2/WPA3-Enterprise with RADIUS for authentication.
Traps to watch
- Sizing APs by coverage only when the space is high-density (auditoriums, stadiums) - capacity governs there.
- Forgetting that 2.4 GHz penetrates walls better but is more congested; do not put high-density clients on 2.4 GHz.
- Confusing RSSI (signal) with SNR (signal-to-noise ratio) - SNR drives modulation and rate.
- Assuming L3 roaming is automatic; it needs explicit mobility configuration.
Rule of thumb
For a capacity design, divide total expected clients by the per-AP client target, then verify the AP count also satisfies coverage. Example: 600 clients in a lecture hall, target 60 clients/AP → at least 10 APs, then confirm each AP's cell edge meets the RSSI/SNR target.