Part of the control traffic that is sent back and forth via LWAPP is information that provides radio resource management (RRM). This RRM engine monitors the radio resources, performs dynamic channel assignments, provides detection and avoidance of interference, and provides the dynamic transmit power control (TPC) that was discussed in Chapter 1, "Introduction to Wireless Networking Concepts." Also, whenever coverage holes (such as when one AP goes down) are detected by another access point, the controller can actually adjust power settings on other APs in the area to correct the coverage hole.
LWAPP can operate in two modes:
■ Layer 2 LWAPP mode: This mode deals only with MAC addresses. This makes sense, because this is the only type of addressing at Layer 2. In Layer 2 mode, the AP needs to be in the same subnet as the controller and hence does not provide much flexibility for large customer installations.
■ Layer 3 LWAPP mode: When operating in Layer 3 mode, the LWAPP can see and use Layer 2 addresses (MAC addresses) and Layer 3 addresses (IP addresses). Layer 3 mode LWAPP allows the network administrator to place APs in different subnet boundaries, and the protocol traverses those boundaries.
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