For managing multiple light weight access point, the Wireless LAN controller(WLC) is used.
A wireless lan controller (WLC) is a device used to manage and control multiple access points called as Light Weight Access Points.In this combination of WLC and LWAP, everything is managed centrally at the WLC.
An autonomous AP does not need a WLC manage it. The configuration, monitoring and troubleshooting etc. is done on the AP itself. If you are using only one AP then there is no problem. But if the company is large and you have to cover a large area of wireless network then you need more than one AP and configuring, monitoring and managing them will be difficult task.
If a client is connected to one AP and he has to move from one AP coverage area to the other AP coverage area then he will be disconnected and connected in the applications he is logged into.
So Cisco has introduced Cisco Unified Wireless Network (CUWN) which is based on centralized control. Cisco Unified Wireless Network (CUWN) consists of a wireless LAN controller(WLC) and Light Weight Access Points(LWAP).
No need to configure the authentication on each and every access point. We can just configure it on the WLC.
Load balancing is provided when the load on one access point is high.
Redundancy is provided when one access point fails, the clients will be still connected to the network via another access point.
In the above diagram-1 you can see that there are three standalone access points. And the user called User1 who is using a Laptop is connected to AP1. Now if he moves out of the coverage area of AP1 and moves into the coverage area of AP2 then the application in which he logged into will be disconnected and connected again.
In the above diagram-2 you can see that the Cisco Unified Wireless Network(CUWN) is used. If the USER1 moves out of the coverage area of AP1 and moves into the coverage area of AP2 then he will not be disconnected in the applications.