Linktrace produces
similar results to, but operates completely differently than, the IP traceroute
capability familiar to the Layer 3 world.
These three functions are specified in great detail in IEEE 802.1ag. Further functions
are described in the ITU-T Y.1731 Ethernet OAM recommendation, though the
equipment specification (G.8021) is not yet complete. Among the most important of
these functions are
?– Alarm indication signal (AIS) An endpoint that detects a connectivity failure
transmits this message toward the user of the EVC to notify the user of the failure.
?– Frame loss measurement Frames can be sent, between the endpoints of an
E-Line EVC only, that allow each endpoint to determine separately for each direction
exactly how many frames have been lost in transit between the endpoints.
410 Chapter 13
?– Frame delay measurement Timestamp information in these messages allow
endpoints to determine how long it takes to convey a frame from one endpoint
to another.
Just as important as the functions themselves, are the context in which these functions
operate. Ethernet CFM/OAM operates in a strictly layered environment (see
Figure 13.
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