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Loopback
Similar to ping at the IP layer, loopback verifies the connectivity between a source device and a
target device. To implement this function, the source MEP sends loopback messages (LBMs) to the
target MEP. Depending on whether the source MEP can receive a loopback reply message (LBR)
from the target MEP, the link state between the two can be verified.
LBM frames are multicast and unicast frames. HPE devices support sending and receiving unicast
LBM frames and receiving multicast LBM frames. HPE devices do not support sending multicast
LBM frames. LBR frames are unicast frames.
Linktrace
Linktrace is similar to traceroute. It identifies the path between the source MEP and the target MP.
The source MEP sends the linktrace messages (LTMs) to the target MP. After receiving the
messages, the target MP and the MIPs that the LTM frames pass send back linktrace reply
messages (LTRs) to the source MEP. Based on the reply messages, the source MEP can identify the
path to the target MP. LTM frames are multicast frames and LTRs are unicast frames.
AIS
The AIS function suppresses the number of error alarms reported by MEPs. If a local MEP does not
receive any CCM frames from its peer MEP within 3.5 times the CCM transmission interval, it
immediately starts sending AIS frames. The AIS frames are sent periodically in the opposite direction
of CCM frames. When the peer MEP receives the AIS frames, it suppresses the error alarms locally,
and continues to send the AIS frames. If the local MEP receives CCM frames within 3.5 times the
CCM transmission interval, it stops sending AIS frames and restores the error alarm function. AIS
frames are multicast frames.
LM
The LM function measures the frame loss in a certain direction between a pair of MEPs. The source
MEP sends loss measurement messages (LMMs) to the target MEP. The target MEP responds with
loss measurement replies (LMRs). The source MEP calculates the number of lost frames according
to the counter values of the two consecutive LMRs (the current LMR and the previous LMR). LMMs
and LMRs are unicast frames.
DM
The DM function measures frame delays between two MEPs, including the following types:
• One-way frame delay measurement
The source MEP sends a one-way delay measurement (1DM) frame, which carries the
transmission time, to the target MEP. When the target MEP receives the 1DM frame, it does the
following:
{ Records the reception time.
{ Calculates and records the link transmission delay and jitter (delay variation) according to
the transmission time and reception time.
1DM frames are unicast frames.
• Two-way frame delay measurement
The source MEP sends a delay measurement message (DMM), which carries the transmission
time, to the target MEP. When the target MEP receives the DMM, it responds with a delay
measurement reply (DMR). The DMR carries the reception time and transmission time of the
DMM and the transmission time of the DMR. When the source MEP receives the DMR, it does
the following:
{ Records the DMR reception time.
{ Calculates the link transmission delay and jitter according to the DMR reception time and
DMM transmission time.
DMM frames and DMR frames are unicast frames.
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