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following MPs: a level 5 MIP, a level 3 inward-facing MEP, a level 2 inward-facing MEP, and a level 0
outward-facing MEP.
Figure 4 CFD grading example
MEP list
A MEP list is a collection of local MEPs allowed to be configured and the remote MEPs to be
monitored in the same MA. It lists all the MEPs configured on different devices in the same MA. The
MEPs all have unique MEP IDs. When a MEP receives from a remote device a continuity check
message (CCM) that carries a MEP ID not included in the MEP list of the MA, it drops the message.
CFD functions
CFD functions, which are implemented through the MPs, include:
• Continuity check (CC)
• Loopback (LB)
• Linktrace (LT)
• Alarm indication signal (AIS)
• Loss measurement (LM)
• Delay measurement (DM)
• Test (TST)
Continuity check
Connectivity faults are usually caused by device faults or configuration errors. Continuity check
checks the connectivity between MEPs. This function is implemented through periodic sending of
CCMs by the MEPs. A CCM sent by one MEP is intended to be received by all the other MEPs in the
same MA. If a MEP fails to receive the CCMs within 3.5 times the sending interval, the link is
considered as faulty and a log is generated. When multiple MEPs send CCMs at the same time, the
multipoint-to-multipoint link check is achieved. CCM frames are multicast frames.
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