# When should an ISP upgrade its backhaul?

Backhaul is easy to leave until it hurts. Upgrade too early and you pay for idle capacity; too late and the busy hour becomes a support queue. The decision is driven by a few measurable things, not by a universal subscribers-per-gigabit rule.

28 March 2026

[ISP & Network Operators](https://netavo.com/insights)

## What actually drives the number

The capacity a backhaul needs is set by the busy hour, not the daily average. Evening peak demand, the shape of your subscriber mix and the growth you expect over the life of the circuit all push the number up, and so does the headroom you keep for a failure, because a link sized exactly to peak has nothing left when a parallel path is lost.

Work it as a transport question. Take your measured busy-hour throughput, add your expected growth over the upgrade's useful life, and add the headroom you need to survive the loss of a redundant path. The result is the capacity to provision. Treat a specific contention target as an input to that calculation, not as a figure to quote without the demand behind it. These are capacity numbers for the pipe, separate from carrier-NAT sizing, which is a different resource measured in ports and state rather than bandwidth.

## Headroom, bursts and the cost of waiting

Two things catch operators out. The first is bursts: short peaks well above the average, from software updates or live events, that a link sized to the mean cannot absorb without queueing and loss. The second is the lead time on an upgrade, which means the decision has to be made before the circuit is full, not when it is.

Netavo provides backhaul and handover from its own core network, on 1G, 10G and 100G ports, so capacity can be stepped up as demand grows and designed with your engineers around your busy-hour profile. The subscriber-facing CGNAT and BNG sizing that sits behind the backhaul is covered separately in the [CGNAT guide](https://netavo.com/insights/cgnat-for-isps).

## Common questions

### Average or busy-hour throughput, which do I size for?

Busy hour, plus growth over the circuit's life, plus headroom to survive the loss of a redundant path. The daily average understates what the evening peak needs.

### Is there a standard subscribers-per-gigabit figure?

No reliable universal one. It depends on your subscriber mix, product speeds and usage patterns. Measure your own busy-hour demand and size from that.

### Is backhaul capacity the same as CGNAT sizing?

No. Backhaul is bandwidth, measured in gigabits; CGNAT is a state-and-ports resource per subscriber. They are planned separately.

## Related services

### [ISP Network Services](https://netavo.com/services/isp)

IP transit, backhaul and L2TP broadband for internet service providers and network operators.

### [Connectivity & WAN](https://netavo.com/services/connectivity)

Fibre and Ethernet access, private WAN and resilient connectivity, from a single site to a national estate.

## Planning a backhaul upgrade?

Tell us your busy-hour demand and growth expectations, and an engineer will talk through capacity and handover options.

[Work with us](https://netavo.com/work-with-us)

Source: https://netavo.com/insights/isp-backhaul-capacity