ISP Bandwidth Oversubscription Calculator
Check an access node's contention ratio: sold capacity versus uplink, busy-hour demand and the throughput each subscriber really gets.
Inputs
Contention Ratio
10.0:1
Busy-Hour Offered Load
7.50Gbps
Uplink Utilisation at Busy Hour
75.0%
Guaranteed Throughput per Subscriber
20.00Mbps
Assessment
Acceptable — plan the next uplink upgrade
Step by step
Values used
Subscribers on the access node = 500 subscribers; Speed sold per subscriber = 200 Mbps; Uplink capacity = 10 Gbps; Subscribers active in the busy hour = 25 %; Average utilisation of an active subscriber = 30 %
ISP Bandwidth Oversubscription
contention ratio = Σ sold speeds ÷ uplink capacity; busy-hour load = Σ sold × concurrency × average active utilisation.
Contention Ratio
= 10.0 :1
Busy-Hour Offered Load
= 7.50 Gbps
Uplink Utilisation at Busy Hour
= 75.0
Guaranteed Throughput per Subscriber
= 20.00 Mbps
Assessment
= Acceptable — plan the next uplink upgrade
How it works
Oversubscription is normal and necessary: subscribers are neither all online nor all saturating their line at once. The contention ratio describes the worst case, while multiplying by concurrency and average active utilisation gives the load the uplink actually has to carry. A 50:1 ratio can be perfectly good service or a nightly disaster depending on concurrency, so the busy-hour figure — not the ratio alone — is what should trigger an uplink upgrade.
Formula
ISP Bandwidth Oversubscription
contention ratio = Σ sold speeds ÷ uplink capacity; busy-hour load = Σ sold × concurrency × average active utilisation.
- concurrency
- Share of subscribers online in the busy hour
- active utilisation
- Average fraction of their sold speed an online subscriber uses
Frequently Asked Questions
How is ISP Bandwidth Oversubscription calculated?
contention ratio = Σ sold speeds ÷ uplink capacity; busy-hour load = Σ sold × concurrency × average active utilisation. Oversubscription is normal and necessary: subscribers are neither all online nor all saturating their line at once. The contention ratio describes the worst case, while multiplying by concurrency and average active utilisation gives the load the uplink actually has to carry.
Why does ISP Bandwidth Oversubscription matter?
A 50:1 ratio can be perfectly good service or a nightly disaster depending on concurrency, so the busy-hour figure — not the ratio alone — is what should trigger an uplink upgrade.
What values do I need to enter?
This calculator takes 5 inputs: Subscribers on the access node, Speed sold per subscriber, Uplink capacity, Subscribers active in the busy hour, Average utilisation of an active subscriber. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.