How broadband works

Downloading videos, sharing holiday snaps or accessing websites in an instant have become second-nature pastimes for many of us, thanks to broadband’s speed and convenience. According to Ofcom, more than 15 million UK households are now hooked up to lightning-fast internet access, but how is 
it all possible?

When imagining how broadband transports data, think of it as a fat pipe carrying water, while dial-up is like a skinny drinking straw. Each can transport the same amount of water, but the fat pipe does the job faster. Similarly, the greater bandwidth of broadband – hence the name – allows for much faster data transfer, making your online experience quicker.

In reality, though, no one installs a huge pipe under your home the day you get broadband. Instead, your copper telephone line is configured so it can carry high-speed data signals alongside your normal voice services. Accessing broadband through telephone lines, known as ADSL (Asymmetric Digital Subscriber Line), is by far the most common connection method, so we’ll concentrate on this when explaining how 
it all works.

How does my phone line deliver broadband to my home?
In the good old days of dial-up access, data was delivered back and forth along your copper telephone line on the same frequency as your voice service. Broadband, which has the capacity to carry more data, runs at a much higher frequency. This is also why you can use voice and data services at the same time.
A device called a microfilter plugs into your phone socket. It splits the voice and broadband signals so there’s no background noise interference on your phone line. The microfilter has a socket for your phone and another for the hardware that allows you to get online.
This hardware could be a basic modem that connects to your PC’s USB port. A combined modem/router that connects to your PC’s Ethernet port is far more stable and secure, however. Routers are used for networking and can be wireless to allow different PCs or laptops around the home to have their own internet connections.

Where does my telephone line 
lead to?
Your copper telephone line leads into your local telephone exchange. Here, a piece of equipment called a DSLAM (Digital Subscriber Line Access Mulitplexer, pronounced dee-slam) turns your data into a digital signal.

The DSLAM can optimise your connection’s performance. If there’s a thunderstorm it might try and put you on a slower, more stable speed, for example. Behind this is BT’s Wholesale network, which uses high-speed fibre-optic cabling to handle the enormous amounts of network traffic. This is where the connection to the internet is made and managed by your ISP.
 
What about ‘unbundled’ services?
More ISPs have been installing their own broadband equipment in BT telephone exchanges so they can control the connection from your home to the exchange. This process is known as local loop unbundling (LLU). This should lead to more competition because ISPs can offer different types of service.

Ultimate speeds still depend on the distance you are from the exchange and the quality of the line, though. New ADSL2+ technology promises to offer better line speeds as it uses a broader frequency range and has better error correction.

 Why does my neighbour get a better speed than me?
There could be a number of reasons. As BT’s Rob Thomas explains: “The performance of your line is dependent on the distance you are from the exchange, the quality of the copper line and the soldering.” If that wasn’t enough, your home’s electrical equipment could interfere with the signal.
Also, beyond your telephone line, you’re sharing your connection with other users at the same time. This measurement is known as a contention ratio (for example, a 20:1 ratio means 20 people are connecting to the telephone exchange using the same line. The lower the first number the better).

However, this figure is becoming less important because ISPs now have a far greater ability to control and shape their traffic. They can tell when you’re browsing the web or doing something more bandwidth-intensive, such as using peer-to-peer (P2P) file-sharing software, for instance. Your speed can also depend on your ISP’s policies as well as on physical or environmental factors. If your ISP has a ‘fair usage’ policy, or if you’re on a package that imposes monthly download limits, it may downgrade you to a slower speed during peak periods.

Is broadband only delivered over phone lines?
No. Virgin Media’s fibre-optic cable network covers around half the country, using the same network of cables that it uses to deliver hundreds of digital television channels. Unlike with ADSL, performance doesn’t vary depending on how far you live from the telephone exchange and the theoretical speed it can deliver data at is much higher.

Mobile broadband is available over the air using high-speed networks such as 3G and HSDPA (High-Speed Downlink Packet Access) where available. With a compatible mobile phone or a 3G card that slots into your laptop or connects to your PC via the USB port, you should be able to send and receive broadband content as easily as you would on a broadband-connected PC at home.

In rural areas without ADSL or 3G coverage, you can get broadband using a satellite that beams data to your own satellite dish. However, you can’t send data back to the satellite, so you will need to have a dial-up connection running alongside it as well.