In a decentralized WLAN structure with stand-alone access points (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 access points. Centralized WLAN management divides these tasks among two different devices:
- The central WLAN controller assumes the administration tasks.
- The decentralized access points handle the data transfer at thePHY layer and theMAC functions.
- 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 WLAN controller.
- Remote
MAC: In this case, all of the WLAN functions are transferred from the access point to the
WLAN controller. Here, the access points only serve as "extended antennas" without
independent intelligence.
- Split
MAC: With this variant, only a portion of the WLAN functions are transferred to the WLAN
controller. Normally, real-time applications will continue to be processed in the access
point; the non-real-time applications are processed via the central WLAN controller.
- Local
MAC: The third possibility provides for complete management and monitoring of the WLAN data
traffic directly in the access points. The only information exchanged between the access
point and the WLAN controller is for network management and ensures that the access points
have a uniform configuration.
The technology from LANCOM Systems 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 WLAN controller 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 WLAN controller. In local MAC architectures the data can alternatively be broken out from the access points directly to the LAN to provide high-performance data transfer. WLAN controllers from LANCOM are also suitable for WLANs that work with the draft IEEE 802.11n standard, so offering much higher bandwidths than previous WLAN technologies. 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.
LANCOM WLAN controllers also support the transfer of payload data through a CAPWAP tunnel.
- This allows selected applications such as VoIP to be routed via the central WLAN controller, 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 WLAN controller (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 WLAN controller.