A potentially interfering node updatable database associated with the MAC, in each node, contains a limited number of unique identification numbers referring to nodes likely to interfere with the transmission of the node. A plurality of panels is attached to the roof structure. A saddle-shaped element is disposable in the slot and has a part cylindrical recess in an upper surface for engagement in use with the rod. A portion of the array of memory cells is coupled for readwrite communication with the controller, and another portion of the array of memory cells is not coupled for readwrite communication with the controller.