ADSL is a kind of broadband Internet connection that you can get over your existing phone line. When people hear about this, they often wonder how on earth it can be true. Doesnt the phone line need to be upgraded? How can all that extra data fit through an ordinary phone line? Why werent they doing this years ago, when I was still dialling up with my old modem? To understand the answers to these questions, its necessary to learn a little about how ADSL works.

ADSL stands for Asymmetric Digital Subscriber Line. The asymmetric part simply means that you can download over the line faster than you can upload good for home users, who generally download (get things from the Internet) far more than they upload (send things to it).

Its the digital part that is important, however. If you think back to old dial-up modems, remember the screeching noises they made when they were connecting? Thats because they were encoding the data they sent over the phone line as sound all those ones and zeros were becoming a series of sounds. It was an analogue to digital to analogue conversion at each end, and was wildly inefficient.

What DSL does is use the unused frequencies of the phone line (that is, the parts that arent needed for voice signals) to carry digital signals, in the form of electrical pulses instead of sound its a successor to ISDN, the expensive business precursor of the technology. This method is much, much faster than the old analogue way. The unused part of the line isnt that big, but DSL splits it up into many smaller pieces and uses each one separately, allowing multiple channels of data to be sent and received at once.

Who said you cant teach an old dog new tricks?