The SCA controller assigns to a unique access point the responsibility of handling downlink transmissions for an individual client station. When the controller receives the incoming transmissions of a client, the SCA controller evaluates the RSSI values of the client’s transmissions. Based on incoming RSSI measurements, the SCA controller can allocate a specific AP for downlink transmissions. The client believes that it is associated to a single AP. However, the client moves between different physical APs based on RSSI measurements evaluated by the controller.

Single-channel architecture is based on a principle of "virtual cells". All APs joined to a virtual cell use the same wireless channel and identify themselves with the same basic service set identifier (BSSID, i.e. a MAC address). The APs in a cell are managed by a centralized Wireless LAN controller (WLC) that coordinates the APs such that APs/transmissions do not interfere with one another. From a client's point of view, a virtual cell appears as a single AP.

The correct answer is C, the APs all share the same virtual BSSID, and the Controller directs which AP to associate with the Client.