Cisco Lightweight Access Point Protocol (LWAPP)
The Cisco LWAPP runs on a WLAN controller and on lightweight access points (LWAPs) to route packets in and out of the WLAN on optimal routes. In other words, the WLAN controller is the gateway of the WLAN to the LAN. The key fact here is that if you do not have a functioning WLC running on your network, none of your lightweight APs will be able to function.
So when your wireless network hits a level that is considered to be mission critical, it is imperative that you have more than one WLC to which your APs can connect. When you configure your APs on your network, you can assign primary, secondary, and tertiary controllers for your network.
If the primary controller is unavailable, the backup controller will be used until the primary becomes available on the network again. And the tertiary controller allows your network when both the primary and backup controllers are unavailable.
Cisco has changed its terminology recently, and LWAPPs are now referred to as controller-based on Cisco parts lists, whereas non-LWAPP or autonomous APs are called standalone.
The controller and APs run protocols that route packets in and out of the WLAN and LAN, using the optimum path through the wireless mesh network and through the wired network linking the WLAN controller to other WLAN controllers. Communication between the LWAP and WLC works equally well at layer 2 with switches or at layer 3 with routers.
When working with the WLC and LWAPs, the LWAPP has a Split MAC function that determines which functions are performed by the LWAP and which functions are performed by the WLC.
The WLC usually performs these functions:
802.11 frame translation and bridging
Termination of 802.11 traffic on a wired interface
The LWAP usually performs time-sensitive operations, such as the following:
Frame exchange handshake between a client and AP
Transmission of beacon frames
Buffering and transmission of frames for clients in power-save mode
Response to probe request frames from clients
Provision of real-time signal quality information to the switch with every received frame
Monitoring each of the radio channels for noise, interference, and other WLANs
Monitoring for the presence of other APs
Encryption and decryption of 802.11 frames
If you have already purchased all your access points and they are autonomous, but you now want to roll out a WLC, then you can convert your APs to Lightweight mode by running a Cisco-supplied upgrade tool on your compatible Cisco AP.
If you decide that you need to re-deploy some of these APs to locations where you are not using a WLC, you can reverse this process by reapplying the latest Cisco IOS for that Cisco AP.