unknown: When the value for this attribute could not be
determined.
direct: Denotes an alarm generated by a set of events where
all events are reported by an observation(s) of a
managed object.
indirect: Denotes an alarm generated by a set of events where
all events were deduced or inferred by the status of
managed objects as determined by the network
management system.
mixed: Denotes an alarm generated by a set of events which
were either direct or indirect.