-Li}- : packet indicating the loss of packet i of a multicast flow M
={M== : multicast flow including the missing packets

+-----------+       +-----+                
|Terminal A |-Li}-+ |     |                           
+-----------+     | |     |      +---------+  +------+
    ^^            +-|     |-Li}--|         |  |Multi |
    ||              | SAT |-Lj}--| Gateway |--|Cast  |
    ===={M==========|     |={M===|         |  |Server|
    ||              |     |      +---------+  +------+
    vv            +-|     |                           
+-----------+     | |     |                           
|Terminal B |-Lj}-+ |     |                
+-----------+       +-----+