HP A5120 EI Configuration Manual page 24

 Test (TST)
CC
Connectivity faults are usually caused by device faults or configuration errors. CC checks the connectivity
between MEPs. This function is implemented through periodic sending of CCMs by the MEPs. As a
multicast message, 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 to be
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.
LB
Similar to ping at the IP layer, LB verifies the connectivity between a local device and a remote device. To
implement this function, the local MEP sends loopback messages (LBMs) to the remote MEP. Depending
on whether the local MEP can receive a loopback reply message (LBR) from the remote MEP, the link state
between the two can be verified. LBM frames and LBR frames are unicast frames.
LT
LT identifies the path between the source MEP and the target MEP. This function is implemented in the
following way—the source MEP sends the linktrace messages (LTMs) to the target MEP. After receiving the
messages, the target MEP 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
MEP. 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 receives no
CCM frames from its peer MEP within 3.5 times the CCM transmission interval, it immediately starts to
send AIS frames periodically in the opposite direction of CCM frames. Upon receiving the AIS frames, the
peer MEP 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), and 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
multicast frames.
DM
The DM function measures frame delays between two MEPs, including one-way and two-way frame
delays.
One-way frame delay measurement
1.
The source MEP sends a one-way delay measurement (1DM) frame, which carries the transmission time,
to the target MEP. Upon receiving the 1DM frame, the target MEP records the reception time, and
calculates and records the link transmission delay and jitter (delay variation) according to the
transmission time and reception time. 1DM frames are multicast frames.
Two-way frame delay measurement
2.
The source MEP sends a delay measurement message (DMM), which carries the transmission time, to the
target MEP. Upon receiving the DMM, the target MEP responds with a delay measurement reply (DMR),
19