Every endpoint listens for the other endpoints??™ CCMs and issues an error
notification if three or more are missed from any other endpoint. This guarantees
the detection of loss of connectivity with a minimum of packets sent. Equally important,
it also detects excessive connectivity, e.g., the accidental concatenation of
two EVCs that are supposed to be separate. This latter capability is an advance
over the OAM capabilities of other Carrier Ethernet technologies.
?– Loopback An endpoint can transmit a unicast loopback message (LBM) to any
other endpoint in the EVC and to intermediate points along the paths among
endpoints. The target point returns the LBM as a loopback reply (LBR). This corresponds
to many other technologies??™ similar capabilities, but the loopback capability
is not used as the primary means for connectivity checking; it is used for fault
isolation after the CCMs detect a connectivity fault.
?– Linktrace An endpoint can issue a linktrace message (LTM) that traces the
route taken by a given target MAC address. Each intermediate point along the
path returns a unicast linktrace reply (LTR) to the endpoint originating the LTM,
so that the originator can construct the path to the target address.
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