WLAN Architecture and Wireless Components

Wireless LAN architecture splits into two models: autonomous (each AP configures itself) and controller-based (a WLC manages many APs). Modern enterprises overwhelmingly use controller-based because it scales — 500 access points centrally managed beats 500 individual config files.

#The Key Components#link

#How a Client Associates#link

1. Client scans channels for beacon frames — APs broadcast these every ~100 ms
2. Client picks an SSID and sends a probe request (or responds to a probe from the AP)
3. Authentication — client proves its identity (open, WPA2-PSK, 802.1X)
4. Association request — client requests to join the AP
5. Association response — AP accepts (or rejects) and assigns an association ID
6. Client gets an IP (usually via DHCP) and begins passing traffic

Beacons are the discovery mechanism — they tell clients what's available. Probe requests are active scanning (client asks 'is SSID X available?'). Both methods work; most modern clients use both to speed association.

#Autonomous vs. Controller-Based#link

• ▪Autonomous AP — full config per AP, no coordination, suited for a handful of APs
• ▪Controller-based — WLC manages config and policy, APs are 'lightweight', suited for scale
• ▪Cloud-managed — controller function in the cloud (Meraki, Mist), modern alternative
• ▪Mesh — APs wirelessly link to each other, used where cabling is impractical

#Check Your Understanding#link