802.3ah Clause 57 (EFM OAM) defines the 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. EFM OAM described in this clause provides data link layer mechanisms that complement applications that may reside in higher layers.
OAM information is conveyed in slow protocol frames called OAM protocol data units (OAMPDUs). OAMPDUs contain the appropriate control and status information used to monitor, test and troubleshoot OAM-enabled links. OAMPDUs traverse a single link, being passed between peer OAM entities, and therefore are not forwarded by MAC clients (like bridges or switches).
The following EFM OAM functions are supported:
EFM OAM capability discovery.
Active and passive modes.
Remote failure indication — Handling of critical link events (for example, link fault, critical event, dying gasp)
Loopback — A mechanism is provided to support a data link layer frame-level loopback mode. Both remote and local loopback modes are supported.
Generation of dying gasp message on access uplink ports on power failure.
EFM OAMPDU tunneling.
Timer for EFM OAM in 500ms interval (minimum).