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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-06
Chapter 39 Configuring Ethernet OAM, CFM, and E-LMI Understanding the Ethernet OAM Protocol
• The OAM sublayer presents two standard IEEE 802.3 MAC service interfaces facing the superior
and inferior MAC sublayers. It provides a dedicated interface for the OAM client to pass OAM
control information and PDUs to and from the client. It includes these components:
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The control block provides the interface between the OAM client and other OAM sublayer
internal blocks.
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The multiplexer manages frames from the MAC client, the control block, and the parser and
passes OAM PDUs from the control block and loopback frames from the parser to the
subordinate layer.
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The parser classifies frames as OAM PDUs, MAC client frames, or loopback frames and sends
them to the appropriate entity: OAM PDUs to the control block, MAC client frames to the
superior sublayer, and loopback frames to the multiplexer.
OAM Features
These OAM features are defined by IEEE 802.3ah:
• Discovery identifies devices in the network and their OAM capabilities. It uses periodic OAM PDUs
to advertise OAM mode, configuration, and capabilities; PDU configuration; and platform identity.
An optional phase allows the local station to accept or reject the configuration of the peer OAM
entity.
• Link monitoring detects and indicates link faults under a variety of conditions and uses the event
notification OAM PDU to notify the remote OAM device when it detects problems on the link. Error
events include when the number of symbol errors, the number of frame errors, the number of frame
errors within a specified number of frames, or the number of error seconds within a specified period
exceed a configured threshold.
• Remote failure indication conveys a slowly deteriorating quality of an OAM entity to its peers by
communicating these conditions: Link Fault means a loss of signal, Dying Gasp means an
unrecoverable condition, and Critical Event means an unspecified vendor-specific critical event. The
switch can receive and process but not generate Link Fault or Critical Event OAM PDUs. It can
generate Dying Gasp OAM PDUs to show when Ethernet OAM is disabled, the interface is shut
down, the interface enters the error-disabled state, or the switch is reloading. It can respond to, but
not generate, Dying Gasp PDUs based on loss of power.
• Remote loopback mode to ensure link quality with a remote peer during installation or
troubleshooting. In this mode, when the switch receives a frame that is not an OAM PDU or a pause
frame, it sends it back on the same port. The link appears to the user to be in the up state. You can
use the returned loopback acknowledgement to test delay, jitter, and throughput.
OAM Messages
Ethernet OAM messages or PDUs are standard length, untagged Ethernet frames between 64 and 1518
bytes. They do not go beyond a single hop and have a maximum transmission rate of 10 OAM PDUs per
second. Message types are information, event notification, loopback control, or vendor-specific OAM
PDUs.