Most Wi-Fi problems are not about Wi-Fi. They’re about how Wi-Fi was deployed: where the access points sit, which channels they’re on, what bands they advertise, and what they tell roaming clients to do. The radio standards have improved dramatically in the past ten years — 802.11ac, ax (Wi-Fi 6/6E), and now be (Wi-Fi 7) all promise huge throughput numbers — and yet most office and home Wi-Fi deployments still feel slow and patchy because the planning didn’t keep up with the silicon. This lesson is about the planning side: the handful of decisions that determine whether your Wi-Fi feels like a wired connection or feels like a 2008 cafe.
This is lesson 17 of Networking from Scratch. We covered Wi-Fi briefly in lesson 6 as “the physical layer when there’s no cable.” This article is the deep dive: the bands, the channel-planning rules, why 5 GHz vs 6 GHz changes more than just the number, AP placement, fast-roaming protocols, and the handful of measurements that turn “Wi-Fi sucks” into a debuggable problem.
The three bands you’ll meet
Wi-Fi runs in unlicensed bands at three different frequencies. Each has different physics — range, penetration, channel count — and the trade-offs drive almost every deployment decision.
| Band | Channels | Range | Congestion | Standards |
|---|---|---|---|---|
| 2.4 GHz | 14 channels, but only 3 truly non-overlapping (1, 6, 11) | Furthest of the three; goes through walls best | Heavy — microwaves, Bluetooth, baby monitors, every cheap IoT device | b/g/n/ax |
| 5 GHz | 25 channels (more with DFS); 24 non-overlapping at 20 MHz width | Medium; one wall is fine, two is iffy | Moderate; cleanest band most places | a/n/ac/ax |
| 6 GHz | 59 channels at 20 MHz; up to 7 channels at 160 MHz | Shortest; line-of-sight is much better than through-walls | Very low — new band, no legacy clients | Wi-Fi 6E, Wi-Fi 7 |
The pragmatic guidance: 5 GHz for the workhorse, 2.4 GHz only for legacy and low-bandwidth devices (think old IoT, garage door openers), and 6 GHz where you have new-enough clients and want max throughput. If your AP supports all three, you’re running tri-band; configure each as a separate radio, not as a unified mush.
Channel planning: 2.4 GHz vs 5/6 GHz
This is the difference that surprises people. 2.4 GHz only has three usable channels. 5 GHz has 25 (or more), and 6 GHz has 59. The size of the “channel-planning problem” is therefore wildly different on each band.
The 2.4 GHz nightmare
Channels 1, 6, and 11 are the three non-overlapping options at standard 20 MHz width. Use any other channel and you’re stomping on traffic in two channels at once. Use 40 MHz channels and you’ve consumed 80% of the band in a single AP.
If you have more than three APs in a 2.4 GHz space, two of them will share a channel. The protocol handles this (CSMA/CA backs off when it detects another transmission), but every AP on a shared channel cuts the available airtime roughly in half. Three APs on channel 6 = each AP gets a third of the airtime. This is why dense 2.4 GHz deployments are universally slow.
Real-world advice: turn off 2.4 GHz on most of your APs. Keep it on a small number for legacy device coverage, and turn it off everywhere else.
The 5 GHz balance
5 GHz has 25 channels (UNII-1: 36, 40, 44, 48; UNII-2: 52, 56, 60, 64; UNII-2C/extended: 100–144; UNII-3: 149, 153, 157, 161, 165). The DFS channels (UNII-2 and UNII-2C) require radar detection — if the AP detects radar, it has to vacate the channel for 30 minutes. Some clients (especially older ones) don’t handle DFS well; some don’t even scan it.
Practical channel plan for 5 GHz at 20 MHz width: 36, 40, 44, 48, 149, 153, 157, 161 — eight non-DFS channels that almost any client can use. Every AP gets one; neighbouring APs get adjacent or non-adjacent channels in a rotating pattern that minimises co-channel interference.
40 MHz wide channels halve the count to four. 80 MHz wide channels halve it again to two. 160 MHz makes the situation untenable in 5 GHz unless you have very few APs — you’d need DFS channels to get more than one. Ironically, the wider channels deliver higher peak throughput per AP but starve neighbouring APs of spectrum, often reducing aggregate throughput in dense deployments. Less is more — default to 20 MHz unless you specifically need wider, and never go above 80 MHz in a multi-AP deployment.
6 GHz: the breathing room
59 channels at 20 MHz, no legacy clients, no microwave ovens. 6 GHz is where you can actually use 80 or 160 MHz channels without starving your neighbours. The catch: only Wi-Fi 6E or Wi-Fi 7 clients can use it, and the range is shorter than 5 GHz. Plan for more APs at lower power, with overlapping coverage so a client never has to fall back to 5 or 2.4 GHz mid-session.
AP placement: the most underrated decision
Where you put the access points matters more than which model they are. Three rules:
- Mount on the ceiling, antenna down. APs are designed to radiate downward and outward in a hemisphere. Mounting on a wall puts half that pattern into the wall. Stuffing one in a closet is worse. The closet ceiling is fine if it’s an open ceiling; a closed mounting closet is a Faraday cage.
- Cover with overlap. Each AP’s usable range at its design throughput might be 15–20 metres on 5 GHz; less on 6 GHz. Plan for cells that overlap at your minimum acceptable signal strength (typically -65 to -70 dBm). The overlap is what lets clients roam without stalling.
- Mind the obstacles. Walls, glass, metal, water (people are 70% water), and especially HVAC ducts kill signal. Two APs in adjacent rooms separated by drywall might both serve their intended areas; two APs separated by a brick wall and a server rack will not.
If you’re deploying anything bigger than a small office, do a site survey: temporarily put APs where you think they should go, walk around with a tool that measures signal strength (Ekahau, Hamina, NetSpot, even a phone app), and adjust before mounting permanently. Time spent on a survey is repaid 10x in fewer help-desk tickets.
Power and density
The instinct “more power is better” is wrong for Wi-Fi. Each AP’s coverage is bounded by the weaker of two paths: AP-to-client (where higher AP power helps) and client-to-AP (where higher AP power doesn’t help — the client can’t shout louder). If the AP can hear the client at -75 dBm but the client can hear the AP at -55 dBm, the link works one way and stalls the other.
The fix: turn AP power down, deploy more APs. Smaller cells with stronger client-side signal beat huge cells with weak client-side signal. Smaller cells also let more clients use higher modulation rates (more bits per symbol) and get off the air faster, which improves overall capacity.
Typical guidance for 5 GHz: 12–17 dBm transmit power per AP, not the 23 dBm or higher that some APs default to. For 2.4 GHz, even lower — 9–14 dBm.
Roaming: the dance between APs
A client moving between APs has to decide when to switch. The 802.11 specs give the client most of that decision: it watches signal strength of nearby APs and roams when the current one falls below some threshold. Three IEEE extensions help the client roam fast:
| Standard | What it does |
|---|---|
| 802.11k | Neighbour reports — the AP tells the client which other APs are nearby and what channels they’re on, so the client doesn’t have to scan the whole spectrum looking for candidates |
| 802.11v | BSS Transition Management — the AP can suggest to a client that it would be happier on AP-X, often used for load balancing and steering bad clients off congested APs |
| 802.11r | Fast Transition (FT) — pre-authenticate the client to the next AP using cached keys, so the actual roam is just a re-association rather than a full 4-way handshake. Roams drop from ~100 ms to ~20 ms |
For a voice/video deployment (SIP phones, Zoom, Teams), all three should be enabled. Without 802.11r, a roam can drop a packet stream long enough to be audible. Some older clients dislike 802.11r; if you have a population of these, enable it on a separate SSID and migrate clients one at a time.
Band steering and minimum data rate
Two AP-side controls that have outsized impact:
- Band steering. When a dual-band client probes for a network, the AP can refuse to answer the 2.4 GHz probe (briefly) so the client moves to 5 GHz. This works on most modern clients. Phones and laptops will end up on 5 GHz; the IoT-grade 2.4 GHz-only devices stay where they belong.
- Minimum basic rate. The AP advertises a minimum data rate that all connected clients must support. Disabling 1, 2, 5.5, and 11 Mbps (the original 802.11b rates) means slow legacy clients can’t connect, but every other client transmits beacons and management frames at 12 Mbps or higher — a 10x airtime improvement on 2.4 GHz alone.
Both of these are off-by-default on consumer gear and on-by-default on enterprise gear. Worth checking either way.
Measurement: turning “Wi-Fi feels slow” into numbers
Three measurements explain almost every Wi-Fi performance complaint:
| Metric | Good | Marginal | Bad |
|---|---|---|---|
| RSSI (signal strength) at the client | ≥ -60 dBm | -60 to -70 dBm | < -75 dBm |
| SNR (signal-to-noise ratio) | ≥ 25 dB | 15–25 dB | < 15 dB |
| Channel utilisation (%) | < 30% | 30–60% | > 60% — congested |
Tools to read them:
- Phone: Wi-Fi Analyzer (Android), Apple AirPort Utility (iOS — needs a setting toggled in Settings > AirPort Utility > Wi-Fi Scanner)
- Linux:
iw dev wlan0 link,iw dev wlan0 station dump - macOS: Hold Option and click the Wi-Fi menu icon — shows RSSI, channel, transmit rate
- Windows:
netsh wlan show interfaces - Enterprise: The AP controller (Aruba, Meraki, UniFi, Mist) shows all of this per-client
If RSSI is good but channel utilisation is high, the channel is overcrowded — pick a less-busy one. If RSSI is bad but utilisation is low, the AP is too far away or too quiet. If both are bad, the deployment needs more APs.
Common mistakes
- One big SSID broadcast on 2.4 GHz / 5 GHz / 6 GHz with the same name. Modern clients pick the best band on their own. Broadcasting it as “Office” on all three is fine. Splitting into “Office-2.4”, “Office-5”, and “Office-6” was a 2010s workaround for clients that couldn’t pick — today it just confuses people.
- Wide channels in dense deployments. 80 MHz on 5 GHz with six APs guarantees co-channel interference. Use 20 MHz; let aggregate capacity beat single-AP peak.
- One AP for everything. A 1500 ft2 apartment with one AP works. A 5000 ft2 office with one AP doesn’t. Plan for one AP per ~1500–2500 ft2 in a typical office, more in dense classroom / lecture-hall settings.
- Disabling Wi-Fi 6 because “old phones don’t support it.” Wi-Fi 6 is backwards compatible. Old clients still connect at 802.11n/ac speeds; new clients get the 6 features. Disabling it just hurts the new clients.
- Mounting AP in a wiring closet because “that’s where the cable goes.” Run a longer cable. The AP belongs above the people, not behind a metal door.
What you can now answer
- Why is 2.4 GHz almost always slower than 5 GHz? — Three usable channels in 2.4 GHz vs 25 in 5 GHz, plus 2.4 GHz collects every microwave and Bluetooth device in the building.
- What channels should I use on 5 GHz? — Non-DFS: 36/40/44/48 and 149/153/157/161, rotated across APs, at 20 MHz width.
- Why does turning AP power down sometimes help? — Smaller cells force higher modulation rates and reduce co-channel interference; client-side signal is the limiting factor.
- Why does my voice call drop when I walk between rooms? — Slow roam. Enable 802.11r to drop the roam time from ~100 ms to ~20 ms.
- What signal strength should I aim for? — -65 dBm or better at the client, with SNR ≥ 25 dB.
- How many APs do I need? — Roughly one per 1500–2500 sq ft in offices; less in lecture halls / classrooms; site survey for anything bigger than a few rooms.
What’s next
Lesson 18 covers the full network troubleshooting toolbox: ping, traceroute, mtr, dig, nslookup, ss/netstat, tcpdump, Wireshark, iperf3, nmap. We’ll go through what each one tests, when to reach for it, and the layer it lives at. Then come the three hands-on labs.