How does ADSL work?

  • Copper wire based connections
  • Good speeds, but not purpose built
  • Currently most stable option for the price

For most people, it doesn't matter how the internet gets to their laptop, as long as it arrives. But when things go wrong, the technical explanation (often delivered after a lengthy wait on hold) only serves to increase the confusion and frustration. For those who want to know exactly what's going on when things go wrong, or anyone who is simply interested in what goes on behind the scenes, here's our guide to how ADSL technology actually works.

The Copper Access Network (CAN)


When the telecommunications network in most countries first rolled out, two lines of copper would be drawn into each property – one to serve, and one redundant. The line would come off the Local Loop, a snake of rubber running a few metres below the city, emanating in a rough circle from an Exchange, which may look like a non-descript building or modest brick home, but inside, contains Pure Liquid Internet (ed. Note- there is no “Pure Liquid Internet”. This is an exaggeration).

For most of this discussion, this is as far as we need to dig to understand how the provision of a home phone service works. But it’s important to note that the rubber tube containing thousands of pairs of copper lines, is a rough circle. Think of this the next time you hear someone arguing that their neighbour can get ADSL, but they can’t, or when someone exclaims they can see their exchange only 200 metres away, but a carrier has told them they’re over 3 km away. The lay of the land above ground has almost nothing to do with the distance belowdecks.

DSL = An imperfect solution

When the need for high-speed internet started to become pressing, running a Digital Subscriber Line (DSL) over the redundant line was an imperfect solution. This is very different from using that extra line for an always on, dial-up connection. Getting into ‘why’ could fill another article, but suffice to say, when a line is activated for DSL, someone in the exchange literally has to remove your line from a normal switchboard, and plug it into a different type of switchboard, and then program the line accordingly. This also goes some way towards explaining why getting an ADSL connection can take weeks; with thousands in the queue and actual, old-fashioned manual labour required, there can be a backlog taking days or weeks to get through.

So why is this imperfect? Well, the technology to run a voice call over a piece of copper is very old, and the copper is very old as well. No-one at the time foresaw the need for a service like the internet to run over that same line. To use another imperfect traffic-based simile: DSL is like opening an emergency highway lane for regular traffic, to ease the load.

So why use it at all? Simple: almost everyone has a phone line, so that infrastructure is already there. There are other options, such as running broadband over your power line – and yes, this has been tried with very limited success in some countries. But the technological barriers were simply too large. Most people also have a connection to the town water supply, but so far, Internet-Over-Mains-Water technology is in its infancy. (ed. Note- there is no such thing as Internet-Over-Mains-Water. The internet is not a liquid).

So DSL was the widespread method for providing the internet ‘signal’ to everyone’s home. The 'A' in ADSL refers to Asynchronous, or uneven. In Australia, we can download much, much faster than we can upload. This is for a number of reasons, but it serves for the moment because few sites are hosted in Australia, while Australia is also a massive consumer of content from sites based far, far away (ie. California). So we need the pull more than we push. For now.

So why can’t I get ADSL?

To provide a phone service, which was the original responsibility of the people who built this copper network, you must be within 5 km of an exchange, and to get around some tricky spots, a host of other technologies were used (pair-gain, RIM, sub-exchanges) to get that phone call to your kitchen handset. ADSL requires that you are much closer. Internet is not quite considered a necessity the same way that a phone line is, and as such, you may find yourself simply too far for even Telstra to provide a service.

What are my alternatives?

ADSL is the most widespreadtechnology for broadband but it's not the only one. Australians are increasingly turning to mobile broadband as an alternative, which transmits the internet data over a mobile phone network. The drawback of mobile broadband is the sometimes patchy coverage, which can lead to drop-outs and slow connection speeds. If you want to investigate mobile broadband, call a few providers and ask about coverage in your area, then choose the provider who has good coverage and a plan that fits your needs. Virgin Mobile (call on 1300 106 571), Optus (1300 785 063) and Vodafone (call Compare Broadband on 1300 106 571) are good places to start.