Wireless (802.11)
Wi-Fi is a shared, lossy, half-duplex medium that behaves nothing like a cable. Most wireless "network problems" are capacity, airtime or interference problems wearing a connectivity costume.
The moving parts
| Term | Meaning |
|---|---|
| SSID | The network name users see |
| BSSID | The MAC of one radio/AP — one SSID can have many BSSIDs |
| Channel | The slice of spectrum a radio uses |
| Band | 2.4 GHz, 5 GHz, 6 GHz (Wi-Fi 6E/7) |
| Airtime | The finite resource: one radio transmits to one client at a time per channel |
| Roaming | Moving a client between APs without dropping the session |
| Standard | Marketing name | Band | Notable |
|---|---|---|---|
| 802.11n | Wi-Fi 4 | 2.4/5 | MIMO, 40 MHz channels |
| 802.11ac | Wi-Fi 5 | 5 | Wider channels, MU-MIMO downlink |
| 802.11ax | Wi-Fi 6 / 6E | 2.4/5/6 | OFDMA, better behaviour with many clients |
| 802.11be | Wi-Fi 7 | 2.4/5/6 | Multi-link operation, 320 MHz |
Why "more bars" is not "more speed"
Signal strength is one input. Throughput depends on:
- Channel width — 20/40/80/160 MHz. Wider is faster and consumes more spectrum, causing more co-channel interference.
- Spatial streams — MIMO count on both ends; a phone with 2 streams cannot use an AP's 8.
- Airtime sharing — 40 clients on one radio each get a slice; adding clients lowers everyone's throughput even at full signal.
- Interference — neighbouring networks, microwave ovens (2.4 GHz), radar (DFS channels), Bluetooth.
- Retries — lossy links retransmit; each retry is airtime spent twice.
A client at −55 dBm on a congested 2.4 GHz channel can be far slower than one at −70 dBm on a clean 5 GHz channel.
Channels, briefly
| Band | Non-overlapping channels | Reality |
|---|---|---|
| 2.4 GHz | 1, 6, 11 | Only three; everything else overlaps |
| 5 GHz | Many, plus DFS | DFS channels must vacate on radar detection |
| 6 GHz | Many, no DFS legacy | Best density, shorter range, needs 6E clients |
"Set every AP to channel 1" is a configuration, not a plan.
Security in one table
| Mode | Status |
|---|---|
| Open | No protection; captive portals only |
| WEP | Broken, never use |
| WPA (TKIP) | Broken, never use |
| WPA2-PSK | Acceptable for home; shared secret does not scale |
| WPA2/WPA3-Enterprise (802.1X) | Correct for organisations: per-user credentials, RADIUS |
| WPA3-SAE | Stronger handshake; protects against offline dictionary attacks |
| WPA3-Enterprise | Best current practice |
WPA2-PSK with a shared password means every departed employee still knows the key, and one leaked key compromises every device.
Roaming and the three helper protocols
Roaming is the client's decision, which is why it is unpredictable.
- 802.11k — neighbour reports, so the client knows what else is nearby.
- 802.11v — network-initiated steering ("this AP is full, try that one").
- 802.11r — fast transition, pre-authenticating the next AP to cut handover time.
Without them, a voice call drops as the client scans and re-authenticates. With them, roaming is usually under 50 ms.
Where it goes wrong
- Designing for coverage instead of capacity. One AP per floor "covers" the floor and collapses under 60 laptops in a meeting room.
- High density with narrow channels and no band steering. Everyone sits on 2.4 GHz because it reaches furthest, which is exactly where there is least spectrum.
- Hidden SSID as security. It hides nothing from a scanner and breaks roaming.
- Captive portals and IoT. Devices without browsers cannot authenticate, which is why guest IoT networks usually need a separate PSK or MAC-based onboarding.
- Assuming Wi-Fi is deterministic. Retries, airtime and interference make it statistical; applications need to tolerate jitter, or the network gets blamed for the app.
- Ignoring the wired side. An AP with a 1 Gbps uplink serving 80 clients at 300 Mbps each is oversubscribed before the first download finishes.
Related Notes
- VLANs Trunking — the wired side of an AP
- Network Security Fundamentals — 802.1X and rogue APs
- Network Design And Topologies — capacity as a design input
- Telemetry And Monitoring — measuring airtime honestly