Hotspot controller or gateway is a hardware device that is responsible for controlling and managing a WiFi network. Usually you need one controller/gateway for managing one WiFi hotspot.
The gateway is responsible for following functions -
- Controlling access to WAN interface / Internet
- Issuing IP to end clients
- AP Management
- Captive Portal
- Interfacing with external AAA server
- Bandwidth control
- Policy control
The gateway/controller is an inline device, and all Internet traffic usually follow through it. The WAN port of the controller is connected to the Internet connection (Fiber, aDSL, Cable Modem, Satellite, etc) and the LAN port is usually connected to the WiFi network.
There are several vendors for WiFi gateways like Cisco, Ruckus, Aruba, HP, Zyxel and many others.