+---+  DATA  +---+
| B |------->| W |
+---+        +---+
              | |
  ------------   -----
 |                    |   +---+
 |              --------->| S |
 |             |      |   +---+
 V             |      |
+---+  data  +---+     -->+---+
|   |------->| W |        | F |
+---+        +---+------->+---+