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- Every packet from every access point must go to the WLAN controller in order to be placed
either on the wired network or back to the wireless network. The WLAN controller decides the
packet’s destiny based on the Cisco-proprietary Lightweight Access Point Protocol (LWAPP)
information that is encapsulated on it. The WLAN controller may analyze the data collected by
the LWAPP-based lightweight access points. LWAPP can control multiple access points at once,
which can reduce the effort for configuring, monitoring, and troubleshooting large WLANs.
- Deploy at least 2 redundant WLAN controllers to avoid the single point of failure. The WLAN
controllers can be managed either at the WCS or the individual controller.
- Traditional WAPs which function on a stand-alone basis are also known as fat or autonomous
APs which contain all wireless processing capabilities. The access points operate in isolation and
the 802.11 traffic is visible to an individual access point only. They are difficult for management,
as they must be managed individually, which can increase operation costs and staffing
requirements. Fat access point deployments are fine for small deployments, but are impractical
for enterprise-class WLAN deployments, which normally supporting hundreds of clients.
Note: There is also a security risk if a fat access point is stolen or compromised.
- Split-MAC architecture splits the processing of the 802.11 protocol between a Cisco LWAPPbased
lightweight (thin) access point that handles real-time aspects of the 802.11 specification
and a centralized Cisco WLAN controller that handles functions that are not time-sensitive.
WLAN
Controller
Switch
Lightweight
AP
Lightweight
AP
Figure 25-5: Split-MAC Architecture Physical and Logical Connections
- Figure 25-5 shows the physical and logical connections between the lightweight access points
and the WLAN controller in the Split-MAC architecture. The access points are not directly
connected to the controller. They are connected to 10/100/1000Mbps switch ports.
Note: Another class of the Centralized WLAN Architecture family is Local-MAC architecture.
- LWAPP defines the following activities that governs the communications between access points
and WLAN controllers:
i) Access point device discovery and authentication. When an access point is being
connected to a WLAN, it uses LWAPP to discover an available WLAN controller in
order to certify itself as a valid network device.
ii) Access point information exchange, as well as configuration and software control.
The access point download and upgrade its software if its code version is differs from the
WLAN controller code version, and configure itself with the appropriate information, eg:
SSID, channel assignment, and security parameters.
iii) Communication control and management between access point and wireless devices.
LWAPP handles packet encapsulation, fragmentation and reassembly, and formatting of
the data that is being transferred between access points and WLAN controllers.
178
WLAN
Controller LWAPP
LWAPP
Lightweight
AP
Lightweight
AP
Figure 25-5A: Physical Connections Figure 25-5B: Logical Connections
Copyright © 2008 Yap Chin Hoong
yapchinhoong@hotmail.com