+---+ +---+ +--+ | | +---+ +---+ +---+ | | +--+ |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