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configured on the ports of device A through device F. Port 1 of device B is configured with the 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 5 CFD grading example
MEP list
A MEP list is a collection of configurable local MEPs and the remote MEPs to be monitored in the same
MA. It lists all 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) with a MEP ID not
included in the MEP list of the MA, it drops the message.
CFD functions
CFD works effectively only in properly configured networks. Its 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)
CC
Connectivity faults are usually caused by device faults or configuration errors. CC examines the
connectivity between MEPs. This function is implemented through periodic sending of continuity check
messages (CCMs) by the MEPs. A CCM sent by one MEP is intended to be received by all of the other
MEPs in the same MA. If a MEP fails to receive the CCMs within 3.5 times the sending interval, the link
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