+---+                               +---+
+--+    |   |    +---+    +---+    +---+    |   |    +--+
|CE|----|PE |----| P |----| P |----| P |----|PE |----|CE|
+--+    |   |    +---+    +---+    +---+    |   |    +--+
        +---+                               +---+

  o-------o----------- Service OAM -----------o-------o

          o----------- Network OAM -----------o

          o--------o--------o--------o--------o  Transport OAM

   o----o   o----o   o----o   o----o   o----o   o----o  Link OAM