802.3ah Clause 57 defines the Ethernet in the First Mile (EFM) OAM sublayer, which is a link-level Ethernet OAM that is supported on 7705 SAR Ethernet ports configured as network or access ports. It provides mechanisms for monitoring link operations such as remote fault indication and remote loopback control. Ethernet OAM gives network operators the ability to monitor the health of Ethernet links and quickly determine the location of failing CFM links or fault conditions.
Because some of the sites where the 7705 SAR will be deployed will have only Ethernet uplinks, this OAM functionality is mandatory. For example, mobile operators must be able to request remote loopbacks from the peer router at the Ethernet layer in order to debug any connectivity issues. EFM OAM provides this capability.
EFM OAM defines a set of events that may impact link operation. The following critical link events (defined in 802.3ah clause 57.2.10.1) are supported:
link fault: the PHY has determined that a fault has occurred in the receive direction of the local DTE
dying gasp: an unrecoverable local failure condition has occurred
critical event: an unspecified critical event has occurred
These critical link events are signaled to the remote DTE by the flag field in OAMPDUs.
EFM OAM is supported on network and access Ethernet ports, and is configured at the Ethernet port level. The access ports can be configured to tunnel the OAM traffic originated by the far-end devices.
EFM OAM has the following characteristics.
All EFM OAM, including loopbacks, operate on point-to-point links only.
EFM loopbacks are always line loopbacks (line Rx to line Tx).
When a port is in loopback, all frames (except EFM frames) are discarded. If dynamic signaling and routing is used (dynamic LSPs, OSPF, IS-IS, or BGP routing), all services also go down. If all signaling and routing protocols are static (static routes, LSPs, and service labels), the frames are discarded but services stay up.
The following EFM OAM functions are supported:
OAM capability discovery
configurable transmit interval with an Information OAMPDU
active or passive mode
OAM loopback
OAMPDU tunneling and termination (for Epipe service)
dying gasp at network and access ports
For information about Epipe service, see the 7705 SAR Services Guide, "Ethernet VLL (Epipe) Services".