This object indicates the source of alarm. The
variable will contain string in the following formats:
'Chassis' indicate the chassis alarms
'Submodule' indicate the submodule alarms
'port@slot#/subslot#/port#'
indicate the port alarms.
NMS app. will need to recognize the above three format
in order to tell the alarm sources. The value other
than the above three format cannot be allowed.