|Planned||Normal downtime that is planed and scheduled in advance.|
|Semi-Planned||Includes software or hardware upgrades that are scheduled, but not entirely by your company.
For example: A vendor released security patches that must be applied quickly to avoid vulnerability. Your company sets schedule, but the schedule is largely driven by others.
|Unplanned||Events that force immediate downtime such as: hardware/software failures; operator error by the administrator; malicious acts, disasters, ISP maintenance windows.|