_________________________________________
        /                                         \
       /        +------+                           \
      |         | PCE  |                            |
      |         +------+                            |
      |                                             |
      |          ***********************>           |
      | +------+           10             +------+  |
CE1 ****| PE 1 | ----- R1 ---- R2 ------- | PE 2 |**** CE2
      | +------+       |        |         +------+  |
      |                |        |                   |
      |                |        |                   |
      | +------+       |        |         +------+  |
CE3 ****| PE 3 | ----- R3 ---- R4 ------- | PE 4 |**** CE4
      | +------+ ***********************> +------+  |
      |                                             |
       \                                           /
        \_________________________________________/