Networker: What does ADSL spell?
It's new, it's exciting, it's wonderful, it's ADSL. Okay, so the marketing departments didn't get to choose the name, but they are certainly leading the latest charge in internet technologies.
ADSL stands for Asynchronous Digital Subscriber Loop. It is a technology used to make a high speed connection between your house and your local telephone exchange, using some smart mathematics and technology. Telstra has been talking about it for a while, and in the US and Britain it is in the process of being introduced.
If you have ever used a modem you will know how painfully slow a home connection to the internet can be, compared to a decent university or business connection.
ADSL is particularly useful in extending the "life" of the copper wires running to hundreds of millions of people's homes around the world. Instead of just a phone conversation or a limited computer connection, you can get a whole lot more of the "new media" services.
The D in ADSL stands for "digital". Your traditional phone service is "analog".
When you speak into your phone your voice sends waves through the air that hit the surface of the phone mouth piece and cause it to vibrate quickly. The position of this vibrating surface is then converted into an electronic "analogy" and carried through the phone system. At the other end this electronic signal is used to make the phone's earpiece vibrate, and the person you are talking to hears your voice.
The only difference with a digital system is that the electronic "analogy" of your voice is converted into tens of thousands of numbers every second, and carried from your phone as a series of numbers. This has the advantage that other things such as videos, music, pictures and e-mail can also be converted to numbers and carried along the same phone line.
"Subscriber Loop" refers to that bit of the phone network between you and the local telephone exchange.
The A is the interesting one. This stands for "asynchronous", which in this case means that the amount of information coming down the line at you is massively larger than the amount of information you can send out, typically 30 times greater. While you can receive more than a million "bits" of information per second, you can only send 64,000 or so, not much better than your current slow modem connection.
The assumption is that as a consumer you will want to buy videos, software, digital television or music and have it sent to you over your phone line. All you will need to send back are some orders for products and a bit of e-mail. You won't want to host your own web site, send a large piece of your own work quickly, exchange large files (such as music files) or collaborate on a large project with a group of like-minded people.
It doesn't have to be like that. The spirit of internet technology is more egalitarian. But then the designers of the internet rules (a haphazard collection of technically minded individuals) don't control phone company policy.
High-speed two-directional traffic is technically feasible, if the phone companies just provide the facilities. But the phone companies want to make money, and the way to do that (they think) is to flog products to consumers.
BY GREG HARRIS