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Getting The Most From ADSL

It's a fair bet that most readers of SILICON CHIP enjoy their daily fix of internet access by courtesy of ADSL. While some readers are luxuriating with optical fibre - and an unhappy minority are still using dial-up - most of us owe our ongoing communication to the distinctly freakish technology of ADSL. But what exactly is ADSL and what came before it? How does it work and why is it often called a "freak" technology? Are your internet speeds painfully slow? Can anything be done to speed them up? Do you curse your ISP? Read on!

By Alan Ford

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Aaahhh - the way we were! This photo, taken in 1981, shows a youthful Dick Smith talking bits and bytes with an equally youthful and then-hirsute Leo Simpson. But the main point about this picture is not so much the all-new System 80 computer and its external floppy disk drive, it's that whizz-bang acoustic modem in which the telephone handset resides. The problem with this (which obviously Dick and Leo didn’t understand) was that the modem needed to be turned on its side to work properly, otherwise the carbon granules in the microphone would tend to coalesce - and cause data loss.

Many of us remember the early days of text-only bulletin boards (which could be regarded as the fore-runners to today’s internet), to which we connected via an acoustic modem.

Bulletin boards were set up in the early 1980s by special interest groups, some businesses and even altruistic individuals. Most specialised in a particular subject or brand and we connected to them by dialling a number specific to that bulletin board. We then carefully inserted the telephone handset into a contraption of cups and flexible joints.

We laid it on its side to prevent
the carbon granules in the microphone from coalescing, moved the cat out of the room to prevent the heavy tread of its paws from interrupting data flow and settled down to enjoy the lightning fast data transfer speed of approximately 300 bits per second (bps).

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A Radio Shack (Tandy in Australia) acoustic modem from the 1980s. These did not work well with the carbon microphone used in Australian telephones at the time.

Without delving into the esoteric realms of parity bits, overhead or consideration of baud versus bits (don’t ask!), you can take that as about 35 characters/bytes per second (8 bits = 1 byte). In practice, various factors contributed to delays (as they do today) and we would usually see text characters emerging on our computer screens one by one or in groups of a few at a time.

How did that old acoustic modem work? Computer binary data streams (well, trickles) would be converted in the modem (or “modulated”) and transmitted over the telephone line as frequency shifted audio tones. At the ISP’s end another modem would convert the sounds to data (or “demodulated”), or vice versa. In fact, that’s where the word “modem” comes from: it’s a MODulator/DEModulator.

That was fine for plain text but then along came graphics, with Microsoft Windows a pioneer (but certainly not the only one), as well as the World Wide Web. Now we needed to access the Web with its rich images and sounds as well.

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