Broadband Contention Ratio: UK Businesses Should Test at 12pm–2pm

Contention ratio is the number of customers sharing the same slice of capacity, and for most businesses it only bites at peak time. If you run video calls, cloud phones or large uploads, check the peak-time speed your provider quotes rather than the ratio itself. Ofcom’s business peak window, 12pm to 2pm, is the standard to hold offers against.

TL;DR:

• Test connection speeds repeatedly from 12pm to 2pm, record results over several weeks, and compare the pattern with the provider’s written minimum guarantee.
• Ofcom’s business code permits exit without penalty if speeds persist below the written minimum and the provider misses its applicable repair deadline.
• FTTP over GPON may share a PON among 30 to 32 customers, while bottlenecks often occur on backhaul or peering.
• Choose a leased line when latency or downtime directly costs money; ordinary office work can use shared fiber with enough headroom and voice priority.

Table of Contents

• What is a contention ratio and how do you work it out?
• Why does peak-time speed matter more than the ratio?
• How does contention differ between ADSL, cable, fibre and leased lines?
• What should you ask at point of sale, and what has Ofcom said about speeds?
• What practical steps reduce contention risk?
• A pragmatic view for small and medium businesses
• Control contention risk with local engineering and support
• FAQ
• Sources

What is a contention ratio and how do you work it out?

A contention ratio compares how many subscribers share a link with the capacity of that link. It is written as subscribers to shared capacity, so 20:1 means twenty customers share the capacity that one customer would use alone.

As an illustration, imagine several offices sharing a link. If they all pulled data at full tilt at the same moment, each would get only a share of the available capacity. That scenario almost never happens.

Here is why the figure misleads:

• Statistical multiplexing: customers send traffic in bursts, so the chance of everyone peaking together is small.
• Averages hide the peak: a low overall ratio can still hide a busy lunchtime.
• Old ratios are historical: textbook numbers such as 50:1 for consumer lines or 20:1 for business lines were rough guides, not performance guarantees.
• Economics drive it: industry observers on the thinkbroadband forum point out that giving every subscriber full peak bandwidth would be prohibitively expensive, so careful planning and monitoring matter more than the headline number.

Why does peak-time speed matter more than the ratio?

Occasional slowdowns are normal. Systemic congestion is different: it repeats at the same hours, on the same activities. Peak-time testing is how you tell them apart.

Ofcom defines business peak time as 12pm to 2pm and residential peak time as 8pm to 10pm. Its business code of practice also expects providers to state a minimum guaranteed download speed at point of sale, and customers can leave without penalty if speeds stay below that minimum and the provider fails to fix the problem within the applicable resolution period.

That 12pm to 2pm window is when contention shows itself in an office. Activities that expose it include:

• Video calls with several participants at once
• Large file uploads or cloud backups running during working hours
• Hosted phone systems carrying many simultaneous calls
• Software updates pulled by many devices together

To spot persistent underperformance, test regularly inside the 12pm to 2pm window over an extended period, record the results, and compare them with your guaranteed minimum. Occasional dips are noise. A pattern is evidence.

Ofcom’s 2025 monitoring report says congestion on fixed networks is generally infrequent, though peak-time constraints can still occur on specific links.

How does contention differ between ADSL, cable, fibre and leased lines?

Where the sharing happens depends on the technology, and so does where the real bottleneck sits.

• ADSL and FTTC: speed depends heavily on the length of copper from the cabinet or exchange, and the connection is contended along the last mile and beyond. Distance often hurts more than contention here.
• Cable: capacity is shared across a neighbourhood segment, though it is provisioned differently from fibre to the premises, so busy evenings can look different from a business lunchtime.
• FTTP over GPON: a passive optical network is shared, and practitioners on the thinkbroadband forums describe practical splits of 30 to 32 customers per PON. Oversubscription tends to show up first on backhaul and peering rather than on the PON itself, and Ofcom’s home broadband performance analysis notes that slowdowns are often a peak-time demand problem on one specific link, not a universal failure.
• Leased lines: dedicated, uncontended bandwidth with stronger service level agreements, suited to revenue-critical services. Our leased lines page explains how these circuits work.

The practical lesson is that “contended” is not a verdict. A well-run shared fibre service can outperform a poorly engineered dedicated one, but only dedicated capacity removes the sharing altogether.

What should you ask at point of sale, and what has Ofcom said about speeds?

Ofcom’s voluntary codes translate neatly into buying questions. The statement on better broadband speeds information explains how “normally available”, minimum guaranteed and maximum speeds should be measured, and says estimates must reflect peak-time congestion. The 2022 business code adds that providers should publish their testing methodology and that you can exit without penalty if the minimum is persistently missed.

Put these questions to any supplier:

1. What speed is normally available during 12pm to 2pm?
2. What is the minimum guaranteed download speed in writing?
3. What remedies and timelines apply if the minimum is missed?
4. How was the figure tested, and is it your own data or the wholesaler’s?
5. What service level agreement and escalation path come with the line?

Pro Tip: Ask for the speed estimate as a range for the peak window, not a single “up to” figure, and keep the written quote with your contract.

What practical steps reduce contention risk?

Contended fibre is perfectly acceptable for general office work: email, web apps, occasional calls. Move to a leased line when downtime or latency costs you money directly, such as a trading desk, a call centre or customer-facing hosted telephony.

Beyond the line itself, a few design choices matter:

• Headroom: buy more capacity than your measured peak, so lunchtime bursts do not saturate the link.
• Traffic prioritisation: set quality of service rules so voice and video outrank bulk transfers.
• Backup connectivity: a 4G or 5G router on failover keeps you online if the main link degrades, and our 5G and 4G routers are built for exactly that role.
• Internal bottlenecks: poor cabling and weak Wi-Fi are often mistaken for contention, which is why a wifi survey is worth doing first.
• Contract terms: secure a minimum speed, service level terms and a clear escalation path before you sign.

After installation, monitor at peak time for several weeks. A managed service such as network monitoring from Abersecure can add round-the-clock alerting.

Pro Tip: Keep your own log of peak-time tests from day one. If you ever invoke a minimum speed clause, dated evidence settles the argument quickly.

A pragmatic view for small and medium businesses

Most small firms overspend on dedicated capacity they do not need, or underspend on the one service that carries their revenue. Reserve leased lines for latency-sensitive or revenue-critical work, and run general office use on good contended fibre backed by a proper SLA. Judge any offer on measured lunchtime performance, never on a raw ratio, and remember that surveys, cabling and local support decide whether advertised speeds arrive.

— Paul

Control contention risk with local engineering and support

We supply business broadband including Basic, Standard and Fibre plans, plus leased lines, 4G and 5G router backup, wifi surveys and network cabling. Professional installations and UK-based support are part of our approach. Request a site survey to discuss connectivity needs for your premises.

FAQ

What is contention in networking?

Contention is the sharing of one pool of network capacity between several customers. It matters when many of them use it at once, which is why peak-time speed is the figure to check.

What is a good speed for fibre broadband?

It depends on how many people and which tasks share the line, so judge it by the peak-time speed your provider quotes. Ofcom’s business code expects a minimum guaranteed speed to be stated in writing.

What is the difference between internet and broadband?

The internet is the global network of networks. Broadband is the fast, always-on connection that carries your traffic to it.

Is it better to have high or low bandwidth?

Higher bandwidth gives more headroom, but it does not fix congestion on a shared link. Match bandwidth to your measured peak demand and check the minimum guarantee.

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