Calculator Inputs
Choose a method, enter your network assumptions, and compute observed, modeled, or target-based availability in one view.
Example Data Table
| Scenario | Method | Period | Maintenance | Downtime / MTBF-MTTR | Availability |
|---|---|---|---|---|---|
| Core WAN segment | Observed | 30 days | 120 min | 36 min downtime, 3 outages | 99.9161% |
| Branch edge router | Observed | 90 days | 180 min | 95 min downtime, 5 outages | 99.9257% |
| Dual-path internet gateway | MTBF/MTTR | 1 year | Not excluded | MTBF 720 h, MTTR 1.5 h, 2 paths | 99.9996% |
| Customer SLA planning | Target | 1 month | 60 min | Target 99.95% | 21.57 min allowed |
Formula Used
1) Observed Availability
Service Window = Total Period − Planned Maintenance
Uptime = Service Window − Unplanned Downtime
Availability (%) = (Uptime ÷ Service Window) × 100
2) MTBF / MTTR Availability
Single Path Availability = MTBF ÷ (MTBF + MTTR)
Parallel Availability = 1 − (1 − Single Availability)n
3) SLA Downtime Budget
Allowed Downtime = Service Window × (1 − Target Availability)
Equivalent Interval Downtime = Interval Minutes × (1 − Availability)
The redundancy formula assumes independent parallel paths. If shared dependencies exist, real-world availability can be lower than the modeled result.
How to Use This Calculator
- Select the calculation mode that matches your analysis.
- Enter the analysis period in minutes, hours, days, weeks, months, or years.
- For observed mode, add planned maintenance, unplanned downtime, and outage count.
- For modeled mode, enter MTBF, MTTR, and the number of parallel redundant paths.
- For target mode, enter the SLA goal to find the downtime budget.
- Click Calculate Availability to display the result under the header and above the form.
- Review the graph, service tier, downtime equivalents, and comparison status.
- Use the export buttons to save the result as CSV or PDF.
FAQs
1) What does network availability measure?
Network availability measures the percentage of service time in which the network remains usable. It focuses on whether service was accessible during the defined operating window.
2) Why exclude planned maintenance?
Many SLAs exclude approved maintenance windows because the interruption was scheduled and communicated. This gives a fairer view of unexpected service loss.
3) What is the difference between availability and reliability?
Availability reflects total usable service time. Reliability focuses on how often failures occur. A system may recover quickly and show strong availability while still failing frequently.
4) When should I use MTBF and MTTR mode?
Use MTBF and MTTR mode when you are planning a design, estimating resilience, or comparing alternative architectures before complete outage history exists.
5) How does redundancy change the result?
Parallel redundancy improves modeled availability because service survives if at least one path remains operational. The improvement depends on independence and similar component behavior.
6) What do the “nines” mean?
The “nines” describe availability classes like 99.9% or 99.99%. More nines mean less allowable downtime over the same period.
7) Can I use this for SLA planning?
Yes. Target mode converts an SLA percentage into an outage budget, helping you define escalation thresholds, maintenance allowances, and expected customer commitments.
8) What do the CSV and PDF exports include?
The exports include the main availability result, downtime equivalents, service window, tier classification, and SLA comparison values shown in the result summary.