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VCAT_LOA was appearing on N2EFS4 board due to the inconsistent of SNCP state

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Issue Description

There is one Ethernet service between two NEs (OSN7500 having software version of Service type is Ethernet Line Service of 2Mbps. Moreover there is configured SNCP between two different lines on SDH layer to protect 2Mbps Ethernet Line Service in case of dual fiber break. The SNCP service is configured NON-Revertive for beow topology.

NE1-NE2-NE3-NE4 (Working path)
NE1-NE5-NE6-NE4 (Protection path)


Alarm Information


Handling Process

After switching the service on NE4 to 'Working Channel' by SNCP Service Control, alams were cleared at the same time. Now the SNCP state becomes consistent and no service alarms are present.

Root Cause

Below points were ensured during troubleshooting and found normal in status

1) The SNCP status was normal for both NE1 and NE4
2) Traffic was not down during these alarms
3) No switching was present for the Ring and SNCP

Later it was found that SNCP service was running on 'Working Channel' on NE1 and 'Protection Channel' on NE4 due to which the trail was showing alarms. Which means that SNCP state was inconsistent. Moreover the traffic was not down during these alarms.


Always make sure that SNCP is in consistent state for both NEs where it is created. Otherwise the signal label to be received at local station is inconsistent with that to be transmitted at the opposite station.

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