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Understanding Broadband Speed

Since the beginning of always-on broadband services, the speed of services has been a constant discussion topic and a central feature of broadband advertising and marketing. The average consumer will usually see one figure, usually prefixed with the words 'up to', but the true quality of a broadband connection can vary significantly from this figure.

This guide will help you understand what affects your broadband speeds, how you can test the speed of your broadband connection, and what you can do to improve it.

What is affecting my speed?

There are a number of different factors which can affect your service speed. Some factors are dependent on the technology used to deliver your connection whilst others affect all types of broadband connections.

In this guide, when we talk of 'ADSL', we are referring to a broadband service delivered over your telephone line which terminates on an ADSL modem/router. 'Cable' services refer to those provided by a cable company such as Virgin Media. There are also other types of services (mobile broadband, wireless services, etc.) so this guide may not cover every possibility.

Things in the home

Between your home and your ISP

ADSL and ADSL2 distance/speed graph

How near you live to your local exchange will affect the speed of your broadband. If you have fibre broadband, your speed shouldn't be as affected by line length.

Between your ISP and the Internet

The Internet is made up of tens of thousands of separate networks; your provider is one of them. When you visit a website hosted on another network, there are a number of possible paths for your traffic to take and sometimes, some of these paths can become congested.

This type of congestion can mean that at times, some websites will appear slow whilst others may be working just fine. It can be caused by your ISP congesting some of their peering links to other networks, or even inside other networks (e.g. those hosting the website you're having difficulty accessing). This is not a reflection on your broadband speed, but something to think about if you are experiencing problems.

Broadband ISP Peering Congestion Diagram
Broadband ISP Peering Congestion Diagram (click to enlarge)

Traffic Management / Shaping

The term 'traffic shaping' or 'traffic management' refers to technology used by providers to control the amount of bandwidth (i.e. speed) available to a particular user, device, application or website. These are commonly used to restrict high volume transfers, either by restricting bandwidth available to the most heaviest users at peak times, or by slowing down certain types of services such as peer-to-peer (p2p) file sharing.

Some types of traffic are less sensitive to speed variations. If you are downloading an operating system update or sending an e-mail, then a delay of a couple of minutes is unlikely to affect your user experience very much. However, if you are watching a live broadcast/television stream, listening to a radio station or having a video chat with someone, an interruption/slow-down can have a noticeable effect. Broadband providers use traffic management technology to sometimes prioritise these applications, to help you get a better experience without requiring additional investment in capacity which would in turn require them to charge more for their broadband service.

Traffic Management / Traffic Shaping on broadband connections

The ASA Rules

Since the beginning of April 2012, the Advertising Standards Authority has adopted a policy which states that where a provider states a numerical speed claim in their marketing communications (i.e. in advertising, on the website, etc.), they should "be able to demonstrate that the speed is achievable for at least 10% of the relevant customer base". This means that if you see an 'up to 14 meg' broadband service, you would expect at least 1 in 10 users to be able to receive 14Mbps.

What is a speed test?

A broadband speed test is a useful tool which you can use to measure the download and upload speed of your broadband connection. It works by measuring the time it takes to download a certain amount of information, and then carrying out the same test in the upstream direction. The measurement is then provided to you along with other information about the quality of your connection.

Our speed test is used by various websites including the Gadget Show because of its reliability, accuracy and our capability to cope with scale. Our speed testing platform has been built from the ground up by our staff for over ten years and uniquely, it runs on a network we control so we can monitor its performance and ensure there are not bottlenecks caused by our end of the connection. Many other speed tests run on shared servers on third party networks, or even on many different networks so the results can vary depending on which server you use. Our test servers are based on dedicated hardware with direct 1Gbps connection to our core network.

The results you receive may vary from one test to the next as the performance of your connection will not always be the same. Please refer to the things affecting my broadband speed section above for more details, and remember the speed test is between your computer and our servers, so make sure it's not affected by anything under your control.

I've done the speed test, what does it mean?

A fast download speed means information will come to you quickly. This means that for example, when you download a music album, it will finish sooner than if you were on a slow connection. A fast upload speed means it's quicker to send information, such as uploading photos or videos to a website.

Broadband speeds are usually measured in "Megabits per second", "Mbps" or "Mb/s" although this is often (incorrectly strictly speaking) referred to as 'meg' or "Mb". Sometimes  you may see speeds in "Kbps" or "Kb/s" which refers to "Kilobits per second". There are 1,000 Kbps in 1 Mbps. Typical broadband download speeds range from a few Mbps through to 100 Mbps for a super-fast broadband service whilst upload speeds range from 250 Kbps (0.25 Mbps) to around 5 Mbps on the super-fast services.

Check the speed your ISP advised you'd be able to get when you signed up. If you're not getting the speed you're paying for, then consider a different provider, but do remember that many of the factors affecting speed may be the same (e.g. your computer, your wireless network at home, the quality of your phone line, etc.) You should raise your concerns with your current broadband provider in the first instance.

Why is my download speed faster than my upload speed?

Since the start of broadband services, download speeds have generally been several times faster than upload speeds. This is called an 'asymmetric' service and it's also the first word in the 'ADSL' acronym. The reason is primarily that with limited bandwidth available, the protocols used have been developed to maximise download speeds as more content is consumed from the Internet than is uploaded to the Internet.

Asymmetric Broadband means that download speeds are faster than upload speeds

There are some technologies such as ADSL2+ Annex-M which increase the upload speeds, but at a cost of slower download speeds. Also, broadband providers can use this imbalance to provide hosting services (which typically use the upload segment) and share some of the cost of running a network between different types of users.

Why is your speed test slower/faster than ... ?

There are a number of differences between our speed test and most others on the Internet. It's worth noting that most other tests run in a similar way, so the fact our tester gives you a different result to many others doesn't mean there's anything wrong with our test.

Here are some of the key differences:

  1. Network—our speed test runs on a network we control giving us the ability to ensure nothing on our end is causing any problems. Some providers run more congested interlinks to the main London peering points such as LONAP and LINX (to which we connect), in which case traffic to us might be affected. The routes to other testers may be different, so they might not be affected in the same way. All our tests run from dedicated servers on our network so we can vouch for our end of the test. Some other testers may pick from a number of servers to pick the fastest ones–We don't believe this is a fair way to measure speed as you get the best result which may not match your true experience when using the Internet.
  2. Traffic shaping—our speed test runs using a custom protocol developed by us. Specifically, this is not using HTTP which is the protocol used for web browsing and which is also used by most other speed tests. We have chosen our own protocol to ensure that we can test the true speed of the connection. Various speed tests using HTTP will give you results which are faster than your line is capable of, often caused by security software which intercepts the connection, breaking the speed measurement system. We let you test over port 80/tcp which is typically used for HTTP, but the protocol is still the same, but sometimes you may notice a difference if your provider is simply filtering certain ports.
  3. Software—our speed test is available either as a Java or Flash version. Most other speed tests are available in Flash only. Sometimes the speed of your computer or the version of Java/Flash can cause problems. This is not necessarily related to the speed of your broadband connection.
  4. Threading—our speed test runs with a single thread which means that it makes one connection to download and upload data. Other testers can use multiple threads to boost speed. Our servers are more than capable of delivering full speeds for broadband connections on a single thread. If you're running an old version of Windows, there are some instances where your settings may mean that a multi-threaded tester performs significantly better, but often the cause of speed issues with single threaded tests are related to your provider's capacity. You can run a multi-threaded test on our download test files below.
  5. Compression—we send random data which has been pre-compressed so that the test reflects the true speed of your connection. Sometimes, it's possible to compress data further and therefore the apparent speed would be faster.
  6. Measurement—we measure the mean average speed of the connection by taking the amount of data transferred and dividing it by the time. Many other testers will measure speed in intervals and show you either the fastest measurement, or a percentile. This means in practice that you could disconnect your broadband service during the test for a few seconds, and then reconnect it, and still get a fast result on some other tests! (yes, we've tried it!). We don't think this is a fair way to represent speed without informing the user.
  7. IPv6—our speed test has been IPv6-compatible for many years. If you have IPv6, you may find routing is a bit different so this can cause a difference. You can run an IPv6 speed test on ipv6-speedtest.net which shows you if you're using IPv4 or IPv6. We also have an IPv6 readiness test to check if your broadband is IPv6 enabled.

Other tools to test speed

In addition to web-based speed tests, we also provide some useful tools you can use to monitor the speed of your broadband connection: