Maintenance window: definition and a practical example
Short answer: A maintenance window is a scheduled, agreed period in which a service may be unavailable for planned work, without failures during that interval being treated as incidents.
In Portuguese: Janela de manutenção
What is a maintenance window?
A maintenance window is a period booked in advance for work that may take the service down: upgrading the IP PBX, replacing the firewall, moving a SIP trunk to another carrier or changing the routing of an 0800 (toll-free) number. During the window an outage is expected and should not be treated as an incident.
The window solves two problems. The first is operational: without it, every test that fails during maintenance fires alerts, wakes the on-call engineer and trains the team to ignore warnings. The second is contractual: many SLA contracts separate scheduled downtime, announced in advance, from unscheduled downtime.
A good window has a defined start and end, covers only the affected circuits and ends with a check. Covering everything “just in case” hides real failures on lines that had nothing to do with the maintenance. And a window that ends without a test misses the most common case: the maintenance is over, but the line did not come back.
In practice
The carrier will migrate the headquarters SIP trunk on Saturday, from 11:00 p.m. to 1:00 a.m. The company has three monitored circuits:
| Circuit | In the window? | Failure at 12:30 a.m. | Failure at 1:15 a.m. |
|---|---|---|---|
| 0800 arriving over the headquarters trunk | Yes | No incident | Incident |
| DID extension at headquarters | Yes | No incident | Incident |
| Branch office IVR, on another trunk | No | Incident | Incident |
The branch office failure at 12:30 a.m. is real and must alert, even with maintenance under way at headquarters. The 1:15 a.m. failure on the headquarters circuits, on the other hand, shows that the migration ended without the trunk coming back.
How Monitor uses this
A maintenance window covers the chosen circuits during a defined time slot. Failures that happen inside it do not open incidents, and the other circuits keep alerting as normal. When the window ends, the following tests open incidents again if the failure persists. See alerts and escalation.
Frequently asked questions
Does scheduled maintenance count against the SLA?
It depends on the contract. Scheduled maintenance, announced with the notice set in the agreement and carried out within an agreed time slot, is commonly excluded from the availability calculation. Outside those conditions, downtime usually counts as normal. Read the clause carefully: notice period, maximum duration, how many windows per month and who can request them.
What is the best time for a maintenance window?
The time with the fewest calls on the affected circuits, which is not always the middle of the night. A 24-hour support 0800 line may be busy at night, while a scheduling IVR gets almost no calls on Sunday. Check call volume before booking, leave a margin for overruns and test the lines right after the window ends.