+--------------------+
      |                    | +---+
      |                    | | C |
      |                    | | T |
      |                    | +---+
+---+ |       Proxy        | +---+   CT = Client Transaction
| S | |  "Higher" Layer    | | C |
| T | |                    | | T |   ST = Server Transaction
+---+ |                    | +---+
      |                    | +---+
      |                    | | C |
      |                    | | T |
      |                    | +---+
      +--------------------+