Fibre fair usage policies: what “uncapped” really means for your business

What a fair usage policy actually is

A FUP is the mechanism that lets an ISP sell “uncapped” plans at a fixed price without a small number of very heavy users degrading the line for everyone else.

Fibre capacity is shared. Your ISP buys bandwidth from a fibre network operator and provisions it across all the customers in your area. If a handful of connections run flat-out around the clock, the contention affects every customer on that segment. The FUP is the ISP’s contractual right to manage that: once your usage crosses a defined threshold, the ISP may reduce your speed, de-prioritise your traffic at busy times, or both.

Two documents matter, and they are not the same thing:

The fair usage policy (FUP) sets usage thresholds and what happens when you cross them. The acceptable use policy (AUP) sets what you are allowed to use the connection for at all; on consumer uncapped products it commonly prohibits running servers, reselling the connection, and, critically for readers of this site, using a home plan for business purposes.

The four levers ISPs actually use

South African ISPs implement fair usage in four broad ways. Most plans combine two or three of them.

1. Threshold throttling

The classic soft cap. Cross the threshold and your line speed drops, on some FTTH products to around 20% of the speed you ordered, until the window resets. Thresholds vary by line speed and package tier; the commonly published range runs from a few hundred gigabytes to about 2 TB on high-speed plans.

2. Rolling windows instead of calendar months

Some ISPs measure your usage over the last 30 days on a rolling basis rather than resetting on the 1st. That matters: one heavy week keeps counting against you for a month, and you cannot “wait for month-end” to recover full speed.

3. Peak-time de-prioritisation

Some products only slow FUP-flagged users while the network is actually busy. Off-peak, you get full speed back. A few ISPs go further and exclude off-peak usage (typically midnight to 06:00) from the FUP count entirely, which is why scheduling backups overnight is more than a folk remedy.

4. Traffic-class shaping

Separate from any threshold, shaped products prioritise interactive traffic (browsing, video calls) over bulk traffic (torrents, large downloads) when the network is congested. An unshaped plan treats all traffic equally; a shaped one does not, regardless of how much data you have used.

The business-use trap in consumer uncapped plans

The cheapest uncapped fibre deals are consumer products, and their acceptable use policies commonly say so explicitly: home and personal use only, business use prohibited.

This is the clause that catches small businesses. A consumer uncapped plan at a home-office price looks like an easy win, but if the AUP prohibits business use, the ISP is within its rights to enforce that: FUP-manage the line aggressively, decline business-grade support, or in principle suspend the service. There is no SLA, no fix-time commitment, and support queues are consumer queues.

Business fibre products cost more for a reason that is mostly invisible on the price card: lighter or no FUP, symmetrical upload speeds, a service-level agreement with defined fix times, and often a static IP. If your VoIP phones, card machines and cloud apps ride on the line, those differences are the product.

What to check before you sign

Five FUP questions separate a plan that will carry your business from one that will embarrass it in month two.

One more check for VoIP users: a throttled line is not just slower downloads. A G.711 voice call needs roughly 100 kbps each way with overhead, which almost any throttle floor can carry, but calls suffer first when a congested, de-prioritised line starts dropping packets. If your phones run over the fibre, FUP terms are call-quality terms.

How to stay ahead of your FUP

If you know how the policy is measured, you can plan around it instead of discovering it mid-quarter.

Keep reading