The theory, and the lab that proves it
Twelve lessons on how Wi-Fi actually works, pitched at the engineer who runs a network but never got taught why. Each one ends with something you can go and measure on an Aruba AP, a Mist AP, and a Sidekick, because a number you measured yourself is the only kind that sticks.
The colour is a nod to the Airheads community. My first expert-level certification came out of an AOS 6 lab and a stack of forum posts by people who answered questions they didn't have to. This section is me paying that forward, one lesson a week.
Frequency, wavelength, and the dBm math you can do in your head. Then a lab where you walk away from an AP and watch the number fall exactly the way the formula says it will.
LabRead RSSI on an Aruba AP and a Mist AP, double the distance, watch it fall about 6 dB. Confirm on the Sidekick.2.4, 5 and 6 GHz, the U-NII blocks, DFS, and what a wider channel actually costs.
LabChange channel width on both platforms and watch client PHY rates and airtime move.EIRP, antenna gain, receive sensitivity, free space path loss. Where the signal goes.
LabPredict RSSI at 10 m, measure it, explain the gap.MCS, coding rate, spatial streams. Why "speed" is a table, not a number.
LabRead MCS in the Central and Mist client views, force a lower rate, measure throughput.Half duplex, contention, PHY rate versus throughput, and the overhead nobody budgets for.
LabAirtime utilisation per SSID, with the mDNS post as the case study.Co-channel and adjacent-channel interference, reuse, cell overlap.
LabTwo APs on one channel. Count retries, watch airtime.Noise floor, SNR, and what a spectrum analyser shows that a Wi-Fi card can't.
LabSpectrum view with a real interferer. RSSI stays put, SNR collapses.Probe, authentication, association, the 4-way handshake, EAP. What happens before the first packet.
LabCapture a join on Mist and on Aruba, then read the same join in ClearPass Access Tracker.Thresholds, 802.11k/v/r, sticky clients, and why the AP can only suggest.
LabA walk test with the Mist client timeline and the Central client events.Clients per radio, cell size, minimum basic rate, application budgets.
LabRaise the minimum basic rate on both platforms and watch the cell shrink.Predictive, AP-on-a-stick, validation. Channel lists and blind spots.
LabA one-room passive survey on the Sidekick, cross-checked against the AP's real channel.Client, RF, infrastructure, upstream. Which tool shows which layer.
LabBreak it three ways and find each one with the right tool.