The theory, and the lab that proves it

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.

A band is a stretch of spectrum, a channel is a slice of it, and width is how big a slice you take. Every doubling of width doubles the rate, halves how many cells you can have, and costs 3 dB. There is a game in here to prove the middle one.

Four numbers tell you how loud your signal will be when it arrives. I wrote the budget for my own lab, walked thirty-two feet, and came up fifteen decibels short with nothing in the way. The gap was real. It was hiding in the one term everybody sets to zero.

The speed of a Wi-Fi link isn't a number, it's a row in a table, and the radio picks a row for every transmission. Neither Central nor Mist will tell you which row. This is how to read it backwards from what they do show, then cap it on purpose and measure what it cost.

Before a Wi-Fi radio starts a transmission, it waits for quiet, draws a random number and counts it down, and every other radio on the channel plays the same game. A laptop linked at 1201 Mb/s that sends one packet per turn moves 55 Mb/s. In the site's model, one old 802.11a/g laptop downloading beside it takes its download from about 720 to about 480.

A reader with twelve APs on one big floor asked whether adding APs makes the edge worse, and whether anything self-tunes. The answer is that AP count was never the variable. Channel width is, and the automation only moves the two knobs you let it.

A client at -67 dBm can be flying or crawling and the RSSI number won't tell you which. The noise floor will. Where the floor comes from, why a Wi-Fi card can't see most of what raises it, and a lab where you raise it yourself with a microwave oven.

A client doesn't connect. It climbs a ladder of a dozen exchanges, and every rung is somewhere it can fall off. This is the ladder in order, what each platform shows you for each rung, and a lab that breaks it three ways so you learn which rung each failure lands on.

The AP never moves a client. It can tell the client who its neighbors are, suggest a better one, or throw it off and hope. What the client is actually doing when it decides, what 802.11k, v and r each change, and a walk test to watch it happen on Mist and Central.

Coverage asks whether everyone can hear the AP. Capacity asks whether everyone gets a turn. The cell isn't drawn by power, it's drawn by the slowest rate you allow, and raising that rate is the cheapest capacity you'll ever buy.

A heatmap is a record of what one instrument heard, on the channels it was told to listen to, on the day. What each kind of survey proves, what the picture leaves out, and the habit of reading the AP's real channel from the controller before you believe the map.

Every Wi-Fi ticket lives in one of four layers, and every layer has a counter that proves it or clears it. This is the method the other eleven lessons were building, and a lab that breaks one AP three ways so you can practice finding each with the right tool.