+--------------+
               |    Control   |
+--------+     | Relay Server |      +--------+
| Data   |     +----+-----+---+      | Data   |
| Relay  |         /       \         | Relay  |
| Server |        /         \        | Server |
+--------+       /           \       +--------+
                /             \        
               /               \
              /                 \
             /  <- Signaling ->  \
            /                     \
      +-------+                +-------+
      |  NAT  |                |  NAT  |
      +-------+                +-------+
       /                              \
      /                                \
 +-------+                           +-------+
 | Init- |                           | Resp- |
 | iator |                           | onder |
 +-------+                           +-------+