ADSL and how to massage your data

Our regular telephone line is a four-boxcar train convoy "running" at becak (rickshaw) speeds. But it runs along tracks that can accommodate a 500-boxcar convoy. But the convoy is very old and in bad condition. Who are you going to call? A symmetrical Digital Subscribers Line (ADSL).

Instead of buying new rolling stock and constructing a new railway, it is best to stick to your old tracks and install at each end the most efficient and fast transshipment and management system on earth. These are ADSL modems. The brains behind these are Digital Signal Processors (DSPs). The system assesses the boxcars' conditions and loads them as they fit. It loads good cars up to capacity, some are a third full, another half full, others 10 percent full, while some are so bad that they go empty.

Every second it sends six million convoys up but only 748 thousand down -- hence the name asymmetrical -- using the same track for both ways, without crashing. That's 200 times faster than the modem you are using. The DSP performs Fast Fourier Transforms. FFT algorithms are used to separate one electrical signal from another or an electrical signal from noise. Some goods arrive somewhat out of shape after this bumpy ride. The DSP can also massage this data -- a kind of shiatsu for bits.

In our railway analogy, we are transporting a large number of goods along a route that for all practical purposes is scrap iron -- in our case scrap copper -- but we get our load across nicely, safely and quickly. By the way, remember that four-boxcar voice line? It is included as well. It means ADSL does not hold your line while you surf. Everybody wins. You get fast connection, your telephone line is not congested, and you can generate revenue from Internet traffic. Only one bill and one provider.

Worldwide, there are 560 million copper lines connecting exchanges to homes. They are growing at 7 percent a year. DSL, as the several kinds of Digital Subscribers Lines are called, are made for them. Stay tuned, because it should have been done a long time ago by ISDN.

OSVALDO COELHO

Bandung, West Java