When all devices in a Fault Domain become unreachable the SpectroSERVER will generate an Unresolved Fault as it is unable to pinpoint the exact cause of the outage.
A 'Fault Domain' is a Group of connected devices. In an ideal world, all your devices would be modeled in the topology showing every
connection along the way. In most cases, due to circumstances beyond our control (devices connected through MPLS, another provider
for which we do not have access to discover) we end up with pockets of connected devices.
example: These 4 devices form a fault domain
When this group of connected devices goes down and they are all unreachable the SpectroSERVER is unable to pinpoint an exact cause.
It could be the Sim1824 that went down or an unmodeled device in the cloud that went down. When this happens the devices are all suppressed and a Critical Unresolved Fault alarm is generated which lists the devices in the fault domain.
The Default Behavior is to create the alarm on the Fault Isolation application model.
example: All devices suppressed
We can see the Critical 'Unresolved Fault' alarm is generated on the Fault Isolation Application Model
To cover another scenario, when Sim18325 is polled and found to not be responding Fault Isolation logic will check its
connected neighbors to see if any of them are up. In this case (below) Sim18324 is up and responding. The Sim18325
device will have been found to be the cause and a Critical Device Has Stopped Responding alarm will be generated on
it. The remaining two devices behind the Sim18325 device are suppressed as they are unreachable due to Sim18325 being down.