+-------+
                ^          | 6LBR  |       |
                |          |       |       |
                |          +-------+       |
        Upward  |         /      /| \      | Downward
        routing |      (F)      / |  \     | routing
                |     /  \    (C) |  (D)   |
                |    /    \    |  | / |\   |
                |  (A)    (B)  : (E)  : R  |
                |  /|\     | \   / \       |
                | S : :    : :  :  :       v