IEEE 802.3ah - OAM

The IEEE 802.3ah, Operations, Administration, and Maintenance (OAM) sublayer, which provides mechanisms useful for monitoring link operation such as remote fault indication and remote loopback control. In general, OAM provides network operators the ability to monitor the health of the network and quickly determine the location of failing links or fault conditions.

Reference:
[1]http://en.wikipedia.org/wiki/OAM
[2]IEEE Std 802.3™-2005
[3]Metro Ethernet Forum. Ethernet in the First Mile Operations, Administration and Maintenance (OAM) – A Tutorial