3ah-compatible EFM technology. The main functions provided by
the EFM OAM include
?– Link performance monitoring
?– Fault detection and fault signaling
?– Loopback testing
OAM is typically optionally implemented in the data-link layer between the MAC and
LLC sublayers, and because it was termed optional in the IEEE 802.3ah standard, system
vendors can use either proprietary or existing management solutions, depending on the
required functions and supported extensions. The EFM OAM can be implemented in
hardware (especially in stations where performance is the main issue, e.g., in OLTs) or
in software (to provide extended flexibility and remote configuration, e.g., in ONUs).
This means that only a certain group of network stations may support OAM features
(e.g., ONUs providing service to premium customers). The OAM functionality can be
implemented on any full-duplex point-to-point (P2P) link or emulated P2P link (EPON
case), and the OAM protocol can be used simultaneously with the 802.3x MAC flow
control PAUSE function, although when doing so, PAUSE inhibits all traffic, including
the OAM protocol data units (OAMPDUs). The EPON OAM protocol is, therefore,
a straightforward implementation of the generic Ethernet OAM protocol, with minor
changes in the MIB targeting adjustment to the EPON environment conditions.
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