Site 1:

[c]
 .
 ........................................> [d]
  +---+ 10 Gbps +---+ 10 Gbps +----+ 50 Gbps
  | A |---------| B |---------| GW |--------- Core
  +---+         +---+         +----+
 ...................
 .                 .
 .                 v
[a]               [b]

Site 2:

[d] <........................................ [c]
  +---+ 5 Gbps +---+ 10 Gbps +----+ 20 Gbps
  | X |--------| Y |---------| GW |--------- Core
  +---+        +---+         +----+
             ....................
             .                  .
             .                  v
            [e]                [f]