Wi-Fi
802.11: association, airtime, and a MAC that is nothing like a switched Ethernet.
Level: beginner
What is it?
Wi-Fi is a family of IEEE 802.11 wireless LAN standards. Stations associate with an access point or operate in supported peer modes, share radio channels, and use link-layer procedures to coordinate transmission and protect frames.
Why does it matter?
Wi-Fi provides mobility without cabling but shares airtime and depends on radio conditions, authentication, roaming, and channel planning. Its performance differs from switched full-duplex Ethernet even when both ultimately carry IP packets.
Mental model
Stations listen and contend for a shared radio medium; acknowledgements and retransmissions help deal with collisions or errors. Throughput is a property of the whole airtime ecosystem, not just an advertised PHY rate.
How it works
- CSMA/CA and link-layer acknowledgements help coordinate use of a shared medium; it is not the same as classic Ethernet CSMA/CD.
- Association connects the station to the WLAN; WPA2/WPA3 security settings determine authentication and encryption behavior.
- Rate adaptation responds to radio quality and retry performance.
- Roaming across APs depends on client decisions, network configuration, and supported 802.11 features.
- Channel interference, adjacent/co-channel networks, walls, and airtime contention can dominate speed.
Steps
- A station discovers the SSID and chooses an AP.
- It associates and completes the security handshake.
- It exchanges data using the selected PHY mode and channel-access behavior.
- If signal quality or AP association changes, it adapts rate or roams while higher-level sessions may continue or recover.
Real-world usage
- Deploying home, campus, and enterprise wireless LANs.
- Troubleshooting retransmissions, roaming, and crowded channels.
Common mistakes
- Assuming advertised Wi-Fi PHY rate equals application throughput.
- Confusing authentication to the WLAN with authorization to every internal service.
- Changing channels or power without measuring nearby co-channel interference.
Interview questions
Why does Wi-Fi use collision avoidance rather than wired Ethernet's old collision detection?
A wireless transmitter generally cannot reliably detect a collision while transmitting; 802.11 coordinates medium access and uses acknowledgements/retries.
Why does client roaming vary across devices?
Clients make roaming decisions using signal, scan behavior, supported features, and vendor algorithms, while AP configuration also influences the process.