Broadband speeds explained: distance, contention & fair use

julia kukiewicz
By Julia Kukiewicz

fastest broadband

There's more to broadband speeds than the headline, as anyone who has battled for bandwidth come 6 o'clock can attest.

This guide will explain how broadband speeds are affected by the lines in your area, the provider's policies and other users.

Actual vs advertised speeds

Before getting into the factors that make up the whole picture on broadband speeds, however, it's important for us to look at why we don't have the whole picture in the first place.

The answer lies in how speeds are advertised and the difference between those adverts and how speeds are actually measured.

How broadband speeds are measured

Broadband speeds are measured based on the number of megabits (basically, blocks of data) downloaded using the connection per second.

On our site we always write this as Mb. Elsewhere, however, you may also see it written as Mb/s, Mbps or even meg.

Speeds under 1Mb are measured in kilobits (Kb) per second. 1Mb is 1024Kb and the typical dial-up connection provides speeds of up to 512Kb.

Speeds over 1024Mb are measured in Gigabits (Gb) per second. 1Gb is 1024Mb.

A broadband speed test will measure both a download speed - which will affect the time it takes to see web pages and, um, download things - and an upload speed - which will affect the time that it takes to upload information, say, photos to a Facebook album - that the device is currently reaching.

In both cases, the speed test is a snapshot of speeds at a particular point in time.

Not only can a single speed test be unrepresentative of a connection's average capacity, it cannot show some aspects of traffic management which mean that the end user will experience certain activities more slowly than others.

Most providers now slow peer-to-peer (P2P) software at peak times, for example.

How broadband speeds are advertised

As of early 2012, broadband speeds are usually but not always advertised as 'up to', meaning a speed that at least 10% of broadband users can achieve.

As people have been saying for years it's an unsatisfactory system.

In Ofcom's broadband speeds voluntary code of practice (of all the ISPs listed on our site, only AOL aren't signed up) Ofcom say:

" is critical that all ISPs explain to consumers that actual throughput speeds are likely to be lower than the headline or advertised speeds..."

So ISPs must also give potential customers an estimated line speed based on the available information about their line and postcode area.

It's that second estimated line speed that broadband customers should refer back to if they're trying to get their broadband up to speed, although it's still only an estimate.

The blame game

When slow speeds are frustrating it's nice to have someone to blame.

We've yet to hear of a broadband user who hasn't suffered from slow broadband speeds at one time or another so our broadband most wanted list singles out the top reasons for slow broadband and explains why they can be a problem.

#1: Your Cables

The truth is that one of the most important factors when estimating broadband speeds - the most important for many users - remains the type of cable installed in the area.

There are five main types in the UK, generally offering :

The fastest - FTTH - is currently only available in the UK as part of broadband trials from BT and Virgin Media or from very small providers like Hyperoptic.

Note that both Virgin Media (more here) and providers using BT's fibre network (listed here) are offering FTTC services but at different speeds, that's partly the providers' decision and partly down to the 'last mile' cables they use. Find out more here.

Because of the expense of installing new technology and because most of the decisions on what to install are being made by profit-making companies, urban areas with more people sharing an exchange are most likely to have the fastest cables installed.

#2: Postcode

The further away a property is from a telephone exchange the weaker broadband signal can become and the slower your actual connection.

This is due to a combination of: attenuation, the signal getting weaker as it moves further away from its source; the quality of the lines themselves and electromagnetic background 'noise' which interferes with the signal.

Fibre optic cable broadband is less prone to attenuation and noise problems which is why it's so much faster than other broadband services.

When people compare broadband by speed, for example using one of our comparison tables (like this one) we filter out services that aren't available at your exchange and also packages offering speeds less than your line can handle - in other words leaving the fastest broadband packages available at the post card and phone number provided.

However, only the providers can give a more specific estimate about how the line should work.

#3: Provider

Intuitively, the best way to throw some broadband blame is at your service provider: after all, you are paying them.

As we noted above, there's a degree of truth to this.

Not only does the provider affect the cables available (see above) and the hardware and contention ratio (below) they can choose to affect connections directly.

Many so-called unlimited deals actually impose a fair use policy on their users.

People who breach the ISP's fair use policy will be 'throttled': it sounds nasty but really it means that broadband speeds are cut to prevent that user from slowing the service down for everyone else.

Most providers' fair use policies only slow the very heaviest downloaders, you can check your ISP's policy here.

In addition, during busy times, usually evenings during the week and afternoons and evenings at the weekends, some providers manage or shape their internet traffic.

In general, downloads, and in particular peer-to-peer (P2P) activity, tend to be slowed during these peak periods.

Almost all broadband providers, including all of the big four ISPs - BT, TalkTalk, Virgin Media and Sky - now publish a standardised version of this information on these restrictions on their websites.

Note, however, that even mobile broadband providers have been known to throttle users.

#4 Hardware

Many deals that advertise higher speeds do so as much on the basis of the hardware - usually a wireless router - that comes with the deal as the broadband itself.

Its important to remember newer - faster - wireless routers will be using the new 802.11n protocol - which means, while they are back compatible, if the wireless card in your computer or laptop was bought a few years ago and only supports 802.11b/g then you won't benefit from the connection speed boost of a wireless 'n' router.

For more on how to check your router see our guide to ways to improve broadband speeds - available here.

#5 Time of day

More people are online between 6pm and midnight - that means less bandwidth per person and slower speeds.

With more people at home during peak times there is also likely to be more noise on the line as a result of people using electromagnetic equipment in their homes which may also slow down your broadband speeds.

There's not much you can do about this as it's a quirk of broadband technology which, unlike water or electricity, isn't just 'off' or 'on'.

All in all, though, if broadband speed really matters switching to one of the fastest broadband deals available is likely going to be the most hassle free way of improving your broadband speeds.

#6 Contention ratio

Finally, the contention ratio describes the number of users sharing one unit of data capacity.

The lower the contention ratio the higher the quality of service. A 50:1 contention ratio would mean that up to 50 broadband customers are sharing the same bandwidth at any one time.

The quality and speed of your broadband connection is dependent on the number of users online at any given time. Business broadband services will often have much lower contention ratios to enable the ISPs to give business users a more consistent quality of service.

The higher the contention ratio the cheaper the broadband package is likely to be - and additionally, different ISPs have different contention ratios. The contention ratio is an important factor involved in the quality and speed of your chosen broadband package.

The average contention ratio for a home user package is 50:1 and 20:1 for a business package. That means that at any one time home users may be sharing their internet access with up to 49 other users all sharing the same bandwidth.

If you are using a 512Kb connection, then, and each of the other users sharing the access are using it at the same time, your connection speed could be reduced to as little as 10Kb!

Fortunately, it's unlikely that everyone uses the connection at the same time.

However, this does highlight the importance of choosing an ISP with a low contention ratio as the fewer people sharing the line, the more bandwidth you potentially have.


23 August 2014

Thanks for the answer.

13 August 2014

Hi, I'm working on the "contention ratio" in broadband internet, would you be so kind to tell me what is the contention ratio in those 5 services mentioned above? How can I get more information from you?

22 August 2014
Choose team

Typically, an ADSL provider's contention ratio used to be 50:1. But we don't actually know the contention ratios of individual providers because they tend not to publish them any more. We think this is because providers have been able to install more capacity (backhaul) at exchanges so there's more differentiation between places and also because fibre, which isn't affected by contention on the exchange level, has become more prevalent.

Sorry that's a bit of a vague answer.

1 May 2014

#1 - half of the story. Yes the cables feeding your pole (or underground directly in a lot of cases) greatly affect your speed, but so does many other factors including your home wiring.
If you have extensions fitted, are using cheap plug and socket extension cables and have connected your router to one of these then the line loss will increase and therefore broadband speed with drop. Equally, houses that use multiple sockets and have fitted the wiring themselves generally have not done it correctly and end up with a 'star wired' or 'backfed' system at their house.

3# 'Not only does the provider affect the cables available' - erm, no. No provider is responsible for the cables from the exchange to your house. That is the sole proviso of Openreach.

6# - contention ratios may, at one time, have been 50:1 for residential customers, but that is far from being the case now with SOME providers at SOME locations. 140:1 and 200:1 can be found at certain exchanges.
Couple this with a DSLAM (broadband equipment in an exchange) having a max throughput of 256mb/s and that being shared with up to 900 customers and you can see why your speed may be lower. (It is unlikely that all 900 ports would be in use, but is possible).
Rule of thumb - you get what you pay for.

#7 REIN, you've skipped over this entirely. Repetitive electrical impulse noise. Essentially noise created by an electrical component like a power supply, or anything that uses electricity, that can induce noise into the cable delivering broadband to your modem.

So what should you do? Yes, pick an ISP with a low contention ratio, but check out your own house.

Does the cable from the pole (or underground) go directly to the socket that your modem is plugged into?
Are there any junction points in your house? (small oval or rectangular boxes) and do they show any sign of corrosion/damp - green coloured irregularity.
Is your line noisy? From small crackles or wooshing noises to 'I can't hear you' noise. A lot of people don't even have a home phone these days, but worth borrowing a phone for a quick check. Noise over the dial tone or during a call will indicate a problem.

Do your own REIN check - tune a radio to 612khz AM/MW. If you hear noise near the cabling that feeds your modem you may have REIN interference. A change in volume as you move the radio will indicate the source - louder it gets the closer you are. Try turning all electrical appliances off first to get a base level to start with.

Call your ISP. They can run checks on your line to identify if any simple faults exist. If it comes back as OK, then ask if they can check your broadband speed and compare it with any of their other customers in the area.
If you've got the money, ask for a broadband engineer to improve your line - chargeable investigation, but you may just end up with faster speeds if your ISP will book an engineer for you.

9 May 2014
Choose team

Thanks for your comments - we didn't put electrical interference in to keep things simple, can't cover everything, but we hope other readers find your comments useful.

To address #1, I think we make clear later on in the article that a number of factors affect speeds. Point #3 is a good one, though. That was poorly worded and has now been corrected.

Thanks again!

28 August 2012

This is a very well composed article. Easy to read and understand. Thanks Julia.