+-----+            +-----+                +-----+            +-----+
|     |            |     |                |     |            |     |
| EE  |<---------->| LRA |<-------------->| RA  |<---------->| CA  |
|     |            |     |                |     |            |     |
+-----+            +-----+                +-----+            +-----+
                                                                    
        synchronous        (a)synchronous       (a)synchronous       
   +----connection----+------connection------+----connection----+   
                                                                    
                                  operators        service partner
+---------on site---------+---back-end services--+---trust center--+

             <--- downstream <--- | ---> upstream --->