Computer & IT
Network Availability Calculator
Estimate redundant-link availability, unplanned path availability, expected downtime, effective service availability, and target gap.
Router availability fraction-
Switch availability fraction-
Single-link failure probability-
Parallel-link availability-
Series path availability before maintenance-
Expected unplanned downtime per year (hours)-
Unplanned plus planned downtime capped at one year (hours)-
Availability after planned maintenance-
Effective minus target availability-
Decision view
Network reliability blocks and availability threshold
Network reliability blocks and availability thresholdRouter, switch, redundant-link block, power, maintenance, and target availability remain explicit.
Exact scenario comparisonSingle access-link availability (%) changes while all other entered assumptions remain constant.
| Single access-link availability (%) | Router availability fraction | Switch availability fraction | Single-link failure probability | Parallel-link availability | Series path availability before maintenance | Expected unplanned downtime per year (hours) | Unplanned plus planned downtime capped at one year (hours) | Availability after planned maintenance | Effective minus target availability |
|---|
How to use Network Availability Calculator
- Enter component availability percentages and number of parallel access links.
- Enter planned maintenance hours and the target availability.
- Use the reliability block and threshold band to identify the weak part of the path.
Calculator guide
Understanding Network Availability Calculator
Network availability is a reliability chain: series components reduce uptime, parallel links improve the link block, and maintenance downtime is added separately.
Calculation method
How the calculation works
Combine router, switch, redundant-link, and power availability under explicit independence and series-path assumptions, then add planned maintenance separately. Convert component percentages to probabilities, calculate parallel-link availability from link-failure probability, multiply the series path, then convert downtime back to availability after maintenance.
Detailed calculation process
Combine component availability and maintenance downtime
The default uses 99.9% router availability, 99.95% switch availability, 99.5% single-link availability with 2 parallel links, 99.8% power-path availability, 4 maintenance hours/year, and a 99.9% target.
General formula: R = r/100S = s/100q = 1-l/100L_p = (1-q^n)100A_u = R S (L_p/100) P 100D_u = (1-A_u/100)8760D = D_u+mA = (1-D/8760)100G = A-T Router, switch, parallel-link block, and power are treated as independent series elements. Planned maintenance is added in hours after unplanned downtime is calculated.
What each symbol means
Worked substitution with the default inputs
The default effective availability is 99.602197%, which is 0.297803 percentage points below the 99.9% target.
Purpose-built visual
Availability reliability block and target threshold
The diagram shows the series reliability blocks, the redundant link block, and the final target comparison band.
Worked situations
Practical examples
- The default uses 99.9% router availability, 99.95% switch availability, 99.5% single-link availability with 2 parallel links, 99.8% power-path availability, 4 maintenance hours/year, and a 99.9% target.
- The default effective availability is 99.602197%, which is 0.297803 percentage points below the 99.9% target.
Better inputs
Useful tips
- Confirm whether the selected prefix uses traditional network and broadcast exclusions or a special point-to-point rule.
- Separate assigned, reserved, quarantined, and growth-reserve addresses before calculating currently available capacity.
- Use integer address counts and verify that used plus reserved addresses never exceed the subnet total.
Before relying on the result
Limitations and common mistakes
- Failures may be correlated; failover time, upstream providers, repair time, software, power diversity, human error, and disasters are not modeled.
- Parallel links are treated as independent.
- Maintenance is added as annual hours, not scheduled windows.
Reference
Key terms
- Series path
- A reliability chain where every component block must be available.
- Parallel links
- Redundant links where the block fails only if every entered link fails.
- Effective availability
- Availability after both unplanned and planned downtime are counted.
Important note
Calculated from the entered technical values using the displayed model. Validate topology, workloads, capacity, security, redundancy, and observed performance before implementation.
Frequently asked questions
Why do series components multiply?
Each component must be available for the whole path to stay available.
Why does maintenance lower availability?
The calculator counts planned maintenance as unavailable service time.
Are redundant links assumed independent?
Yes. Shared ducts, providers, or devices would reduce the real benefit.
What does a negative target gap mean?
The effective availability is below the entered target.