-{}- : bidirectional link

                        +---+    +--------------+
                   +-{}-|SAT|-{}-|BACKBONE      |
+----+    +---+    |    +---+    |+------------+| 
|End |-{}-|CPE|-{}-|             ||CONCENTRATOR||
|User|    +---+    |    +---+    |+------------+|    +-----------+
+----+             |-{}-|DSL|-{}-|              |-{}-|Application|
                   |    +---+    |              |    |Server     |
                   |             |              |    +-----------+
                   |    +---+    |              | 
                   +-{}-|LTE|-{}-+--------------+              
                        +---+