Subscriber Capacity & Oversubscription Calculator
Model how many subscribers an uplink really supports using peak-hour concurrency and average usage, rather than a contention ratio someone invented.
Result
Sensitivity to concurrency assumptions
| Concurrency | Peak demand | Utilisation | Max subscribers |
|---|---|---|---|
| 20% | 3.20 Gbit/s | 32% | 4,375 |
| 30% | 4.80 Gbit/s | 48% | 2,916 |
| 40% | 6.40 Gbit/s | 64% | 2,187 |
| 50% | 8.00 Gbit/s | 80% | 1,750 |
| 60% | 9.60 Gbit/s | 96% | 1,458 |
| 70% | 11.2 Gbit/s | 112% | 1,250 |
About Subscriber Capacity & Oversubscription Calculator
Oversubscription is unavoidable and, done with real numbers, entirely safe. The failure mode is planning against sold capacity - or against a contention ratio inherited from a decade ago - instead of against measured busy-hour demand.
Measuring instead of guessing
The two inputs that drive this model — busy-hour concurrency and average demand per active subscriber — are measurable, and measuring them beats any industry rule of thumb. Take 95th-percentile interface throughput at the aggregation point over a month, divide by the subscriber count on that interface, and you have your real per-subscriber busy-hour figure. Track it quarterly: it has risen every year for two decades, and a capacity plan built on last year’s number is already behind.
The numbers that actually matter
Two figures drive everything: what fraction of subscribers are active in the busy hour, and what each of those averages. Residential broadband typically sees 30-50% concurrency at peak with 3-12 Mbit/s average demand, dominated by adaptive-bitrate video which backs off gracefully. Business connections run higher concurrency and are far less tolerant. Plan speed barely enters the calculation - a 1 Gbit/s subscriber watching television consumes 15 Mbit/s.
Common use cases
- Deciding when an uplink upgrade becomes necessary.
- Sizing a new PoP or sector before committing to hardware.
- Testing how sensitive a plan is to concurrency assumptions being wrong.
Edge cases and gotchas
- Busy-hour demand grows year over year - build in growth, not just headroom.
- A single large game or OS release can double peak demand for a day; headroom is what absorbs it.