by Chris Woodford. Last updated: April 25, 2017.
If you're still using a dial-up modem to access the Internet, switching over to broadband (fast, always-on Internet access) will seem like nothing short of magic. Not only does your Internet access become many times faster, but you can use your telephone line at the same time as well (something you can never do with dialup). Broadband sweeps you from the dirt tracks to the freeway—and leaves the 21st-century information age lying at your feet! But how exactly does it get so much more Internet power from exactly the same piece of telephone cable?
Photo: A typical broadband modem made by Netgear: the piece of equipment that lets your computer make a broadband connection to the Internet. The long white bar sticking out of the back is a wireless antenna (aerial).
Telephones were never made for the Net
Before the Internet came along, the world of computing was a very different place. There were far fewer computers and they worked mostly in isolation or in small networks known as LANs (local area networks). The Internet has increased the power of people's computers many times by allowing all these machines to talk to one another and exchange information via such things as e-mail and file sharing. You might wonder where the Internet came from; it seemed to take off virtually overnight. In fact, the vital piece of infrastructure on which the Net is built was already in place and had been invented back in the 1860s. I'm referring, of course, to the telephone system.
When Alexander Graham Bell and others pioneered telephones in the 19th century, their idea was to help people talk to one another over long distances in "real-time." Although telephone equipment was designed for carrying sounds, it gradually became obvious that the technology had many other uses. During the late 20th century, for example, many people started using a technology called fax (facsimile), which transmits printed documents between two electronic machines, one at either end of a telephone line. When computer networks began to take off in the 1970s, it was perfectly natural to use the telephone system to connect them together. But this created an immediate problem: computers exchange information (data) in a number-based form known as digital, whereas the telephone system had always been designed to handle rapidly changing sound waves or analog information. How could computers and telephones be made to understand each other?
Photo: A pair of old-style dialup modems. The dark box on the bottom is a typical 56K dialup modem from the 1990s. On top is a 56K credit-card-sized PCMCIA modem for use in a laptop.
How dial-up Internet works
The answer turned out to be surprisingly simple. If you go on holiday to a foreign country where you can't speak the language, you have two choices. One is to shout, wave your hands around, and point excitedly. A much better option is to get yourself a translator, who can convert your words smoothly and seamlessly back and forth into the foreign language. This second approach is the one that computers use when they want to exchange information over the old-fashioned telephone network. But instead of using a translator, they use an electronic "translating" device called a modem.
A modem (which is short for modulator-demodulator) takes the digital information that your computer generates and turns it into analog information (up and down, constantly varying sound waves) that can travel along the telephone network to another computer somewhere else. At that other location, there is another modem that converts the incoming analog information back into digital data that the other computer can understand. Two computers can have a lengthy conversation over the phone, just like two people chatting away, providing there is a modem at each end of the line to translate the digital information they generate into analog signals that can travel back and forth along the telephone line. (Incidentally, if you're uncertain about the difference between analog and digital, we have a simple article about analog versus digital technology.)
When you dial into the Internet, what you are actually doing is using a modem and telephone line to make a semi-permanent connection into a much larger computer network. As your computer dials in, it sends digital information down the telephone line to a modem at your Internet service provider (ISP). Once your modem is talking to the ISPs modem, your computer can use the ISP's computer to access other computers all over the Internet. Every time you browse a web site, your computer is making a link to another computer somewhere else on the planet using your ISP's computer as a stepping stone.
How is broadband Internet different from dial-up?
Dial-up is a really inefficient way of linking to the Internet. When you dial in, your computer telephones your ISP's computer and then hogs the line for the duration of the call (in other words, for as long as you're online). No-one can call you on the phone while you're online. And even though your computer is hogging the entire line, your modem and the ISPs modem exchange information at very low speeds—at best, approximately 56Kbps (roughly 56,000 bits or binary ones and zeros) per second. If you're trying to download MP3 music tracks or digital photos, you'll know this is grindingly slow and tedious. A single music track can take half an hour or more to download.
Broadband works a completely different way. Instead of treating your phone line as a single, narrow pipe between your computer and the ISP's computer, like a dialup connection, it divides the line into many different channels. Information can travel in parallel streams down these channels. It's like dividing a highway into several lanes: lots more traffic can go down it in parallel than down a single-lane road. This is why broadband is so much faster than dialup. Even a slowish broadband line, working at 512Kbps, is about nine times faster than the best dialup connection, while a moderately fast broadband line, working at around 8MBps (megabits per second), can be over 100 times quicker!
Artwork: Dialup and broadband use the same phone line, but broadband uses it much more efficiently. Where dialup sends only one voice or data signal down one channel, broadband divides the line into multiple channels, each of which can send data in parallel. Most channels (red) are used for downloading; a few are reserved for uploading (blue). You can also have a phone conversation at the same time (using the green channel).
Most people download far more information than they upload (browsing web pages is almost exclusively downloading—because most of the data is flowing into your computer from the Net), so broadband allocates more channels to downloading than to uploading. This is why broadband computers download several times faster than they upload. In other words, downloading and uploading are not equivalent or "symmetrical" processes: they are asymmetric. That's why the technical name for this type of broadband is Asymmetric Digital Subscriber Line or ADSL. Another type of broadband called DSL allows uploading and downloading at the same speed.
If most people are just downloading, why doesn't broadband Internet scrap the uploading channels altogether and make browsing even faster? Any type of web browsing involves a certain amount of two-way traffic between your computer (which is called a client) and the remote computers (servers) that host the pages you're looking at. Even though most of the data is flowing into your computer, a certain amount still has to flow in the opposite direction each time your computer requests a new page. In other words, even when all you're apparently doing is downloading, there's some uploading going on in the background to make that happen.
That just leaves one more question: how can you talk on the phone while your computer is simultaneously sending and receiving data? Simple. Some of the channels on the line are reserved for phone calls. People's voices use relatively low-frequency sounds, compared to the higher-frequency signals that computer modems use, so it's relatively easy to keep the phone signals separate from the computer data.