Use this procedure to request the MEP to begin a proactive Loss Measurement session for a particular Class of Service, using CCM frames (ethoam mep mep-cc). The results are minimum, maximum, and average, near end and far end, Frame Loss Ratio (FLR) per 15-minute and 24-hour intervals, reported via SNMP. In addition, SES and UAS PM are augmented by per-second FLR calculations.

Loss Measurement provides an accurate accounting of frames received versus frames sent for a service. A typical use is by a Service Provider who conducts the measurement proactively (continuously) end-to-end for Service Level Agreement (SLA) verification. Up-MEP’s at the service endpoints exchange frame count information to make the calculation. The customer can do the same in their equipment for the same reason, using Down-MEPs on their UNI ports. If the service crosses administrative boundaries, then the responsible entities may measure performance on each leg, bounded by their MEPs.

Proactive LM is also used to monitor Severely Errored Second (SES) and UnAvailable Second (UAS), also for SLA verification. An FLR is calculated each second, and if it exceeds 75%, (or if the MEP detects a direction-relevant fault) then the SES counter is incremented. UAS is calculated in the same manner as in TDM. Both are implemented according to ITU-T G.7710.

Proactive results are only available by SNMP. A TCA notification is provided for LM and DM current maximum and average FLR bins, and for SES and UAS. The thresholds are user configurable. See Proactive LM Threshold parameters.

Refer to the following restrictions:

• Ethernet OAM pm (ethoam pm) must be enabled. See Procedure 16-4.1: Enable Ethernet OAM Performance Monitoring (PM).

• Proactive LM can be configured on only one Up-MEP for a particular VID and priority, and on only one Down-MEP for a particular VID, priority and port.

• You cannot enable a proactive LM session on both an Up and Down MEP having the same VID and priority.

• You can enable proactive LM simultaneously with on-demand LM and an on-demand LM responder, for the same VID and priority, but they must all be on the same MEP.

• The MEP must belong to a VLAN and have CCM enabled.

• The remote peer MEP should also have proactive LM enabled.

Note:

Protection schemes which replicate broadcast, unlearned unicast, or multicast traffic (call any of these MC) may be incompatible with accurate Y.1731 Loss Measurement (LM) on the VLNC42x.

ERP and RSTP are two examples. If the NE has two (or more) unblocked ports, MC traffic is replicated and sent out each port. The LM Tx counter increments for each replication of monitored frames. However, the remote end receives only one of the replicates. A comparison of LM local Tx and remote Rx counts shows apparent frame loss when none has occurred. Additionally, when the remote end sends MC traffic, the NE with unblocked ports also counts those, because they are passed through.

For example ERP uses two ports. Assume proactive LM is active at MD level 4 and a MEP at MD level 5 has CCM enabled at 1 second intervals. Then, the proactive LM Tx count includes two replicate CCM's generated by the local MEP at level 5 and one pass-through CCM from the remote MEP. The remote MEP receives and counts only one. If this were the only traffic, then the reported FLR would be a constant 67%. In a working network, the degree of inaccuracy depends on the mix of unicast and MC traffic. During times of no MC traffic, the accuracy is 100%.

On-demand LM is similar. Its Tx count includes CCM at the same MD level, in addition to those of levels above.