A Wireless LAN Controller (WLC) is a piece of hardware that communicates with and manages a large number of lightweight APs using the IEEE CAPWAP (Control and Provisioning of Wireless Access Points) protocol, which is based on Cisco's Lightweight Access Point Protocol (LWAPP). CAPWAP carries both control traffic (DTLS-encrypted) as well as data traffic (DTLS encryption optional) between the APs and Controller.
APs can be deployed in standalone or centralized mode.
- Standalone: As the name suggests, in this mode, APs are deployed and maintained individually. This is the most commonly seen type of deployment in small/medium businesses, where only a few APs are needed.
Figure 9.3: Wireless APs in standalone mode
- Centralized: In this mode, large number of APs are managed by wireless LAN controller(s) for their device configurations, security/policy settings, software/firmware updates and so on. The connectivity between the APs and Controller can be either via a layer 2/3 network. As mentioned earlier, APs are managed by wireless controller using CAPWAP protocol, which handles both data as well as control traffic.
Figure 9.4: Wireless APs in centralized mode
With a basic understanding of wireless LAN devices, let's look into a few more terminologies used in wireless:
- STA: Wireless station or client using the service
- AP: The device providing wireless service to the clients
- DS: Distribution, the LAN that connects the APs
- BSS: Basic Service Set (BSS), or units of wireless devices operating with the same media characteristics (for example, radio frequency and modulation scheme)
- ESS: Extended Service Set (ESS), or logical units of basic service set(s) in the same logical network segment (for example, IP subnet and VLAN)
Refer to the following diagram for a better understanding of these terminologies:
Figure 9.5: Wireless LAN distribution and service sets