Make note that there's a difference between ONT-MISSING and ONT-DYING-GASP.
ONT-MISSING: The ONT unexpectedly fell off the network (like a fiber cut).ONT-DYING-GASP: The ONT was powered down and sent a gasp right as it noticed it lost power.
The distinction between these two alarm types is what will save lots of time in further troubleshooting.
A dying gasp from a single ONT could simply be an end-user unplugging their ONT for the night or leaving town for a while. If dying gasps come in a large bunching, let's say it's a distinct region of the overall service area, it could be inferred there is a power outage that caused all the ONTs in that area to power down.
A missing alarm is more concerning. Depending on the correlation of ONTs falling off the network and which PONs are affected, this could indicate different levels of fiber cut or even faulty hardware/software.
Check the following:
- PON Status
Consider bouncing the PON port.
Make sure the system didn't shutdown the port for some reason (system-disabled status).
- ONT Tab
On the PON's page, check the ONTS tab to verify the light status on the affected ONTs. It has been a known issue in the past that there is a bug that will cause ONT status to not make it back to the OLT causing them to appear offline when they aren't. Because of this, check other PONs on the same card and on different cards to verify the latter is likely not the issue. (Generally, bouncing the PON port or rebooting the card would resolve this bug)