-{}- : bidirectional link
C : where Network Coding techniques could be introduced 

+---------+    +---+    +--------+    +-------+    +--------+
|Satellite|    |SAT|    |Physical|    |Access |    |Network |
|Terminal |-{}-|   |-{}-|Gateway |-{}-|Gateway|-{}-|Function| 
+---------+    +---+    +--------+    +-------+    +--------+
     C                       C            C           C