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EFM-OAM protocol
The functionality of the EFM-OAM can be summarized under the following categories:
• Discovery: Discovery is the mechanism to detect the presence of an OAM sub-layer on the remote
device. During the discovery process, information about OAM entities, capabilities, and
configurations are exchanged.
• Remote fault detection: Provides a mechanism for an OAM entity to convey error conditions to its
peer by way of a flag in the OAMPDUs.
• Remote loopback: This mechanism is used to troubleshoot networks and to isolate problem
segments in a large network by sending test segments.
Discovery
Discovery is the first phase of EFM-OAM. At this phase, EFM-OAM identifies network devices along
with their OAM capabilities. The Discovery process relies on the Information OAMPDUs. During
discovery, the following information is advertised through the TLVs within periodic information
OAMPDUs:
• OAM capabilities: Advertises the capabilities of the local OAM entity. Using this information, a peer
can determine what functions are supported and accessible (for example, loopback capability).
• OAM mode: The OAM mode is conveyed to the remote OAM entity. The mode can be either active or
passive, and can also be used to determine a device’s functionality.
• OAMPDU configuration: This configuration includes the maximum OAMPDU size to delivery. In
combination with the limited rate of 10 frames per second, this information can be used to limit the
bandwidth allocated to OAM traffic.
Timers
Two configurable timers control the protocol, one determining the rate at which OAMPDUs are to be
sent, and the second controlling the rate at which OAMPDUs are to be received to maintain the
Discovery procedure from resetting.
• The timer should generate PDUs in the range of 1 through 10 PDUs per second. The default value is
1 PDU per second.
• The Hold timer assumes the peer is dead if no packet is received for a period of 1 through 10
seconds. The default value is 5 seconds.
Flags
Included in every OAMPDU is a flags field, which contains, besides other information, the status of the
discovery process. There are three possible values for the status:
• Discovering: Discovery is in progress.
• Stable: Discovery is completed. Once aware of this, the remote OAM entity can start sending any
type of OAMPDU.
• Unsatisfied: When there are mismatches in the OAM configuration that prevent OAM from completing
the discovery, the discovery process is considered unsatisfied and cannot continue.
Process overview
The discovery process allows local Data Terminating Entity (DTE) to detect OAM on a remote DTE.
Once OAM support is detected, both ends of the link exchange state and configuration information
(such as mode, PDU size, loopback support, and so on). If both DTEs are satisfied with the settings,
EFM-OAM protocol
FastIron Ethernet Switch Administration Guide 115
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