In a decentralized WLAN structure with stand-alone APs (operating as so-called "rich access points") all functions for data transfer take place in the PHY layer, the control functions in the MAC layer, and the management functions are integrated in the APs. Centralized WLAN management divides these tasks among two different devices:
- The central WLC assumes the administration tasks.
- The decentralized APs handle the data transfer at the PHY layer and the MAC features.
- A RADIUS or EAP server can be added as a third component RADIUS or for authentication of WLAN clients (which can also be the case in stand-alone WLANs).
CAPWAP describes three different scenarios for the relocation of WLAN functions to the central WLC.
- Remote MAC: In this case, all of the WLAN functions are transferred from the AP to the WLC. Here, the APs only serve as "extended antennas" without independent intelligence
- Split MAC: With this variant, only a portion of the WLAN functions are transferred to the WLC. Normally, realtime applications will continue to be processed in the AP; the non-realtime applications are processed via the central WLC.
- Local MAC: The third possibility provides for complete management and monitoring of the WLAN data traffic directly in the APs. The only information exchanged between the AP and the WLC is for network management and ensures that the APs have a uniform configuration.
Smart Controller Technology from LANCOM uses the local MAC procedure. Thanks to the reduction of centralized tasks, these WLAN infrastructures offer optimum scalability. At the same time, infrastructure of this type prevents the WLC from becoming a central bottleneck that has to process large portions of the overall data traffic. In remote MAC and split MAC architectures, all payload data is forced to run centrally via the WLC. In local MAC architectures the data can alternatively be broken out from the APs directly to the LAN to provide high-performance data transfer. With break-out into the LAN, data can also be directly routed into special VLANs. This makes it very easy to set up closed networks, such as for guest access accounts.
Layer 3 tunneling and layer 3 roaming
WLCs with LCOS also support the transfer of payload data through a CAPWAP tunnel. This allows selected applications such as VoIP to be routed via the central WLC, for example. If WLAN clients change to a different radio cell, the underlying IP connection will not be interrupted because it continues to be managed by the central WLC (layer-3 roaming). In this way, mobile SIP telephones can easily roam between Ethernet subnets, even during a call.
Managing data streams centrally can also make configuring VLANs at the switch ports unnecessary in environments with numerous VLANs because all CAPWAP tunnels are centrally managed on the WLC.
