It was claimed to be impossible. Achieving a data rate of 33.6 kbit/s was hard enough, it was said. The old analogue telephone system could not carry any more.
Now that has changed. Several modem manufacturers are offering 56 kbit/s modems, and some are promising upgrades to older devices. If 33.6 kbit/s was so difficult, how can a 66% increase be achieved? How do these new modems work, and will they be as fickle as the current ones?
This article aims to answer these questions, by describing how the new modems work and where their limitations lie. For these modems are new - they employ many entirely new techniques to approach the ultimate limit for data transfer through the telephone network.
The popularity of the Internet has generated a huge market for fast modems. Until alternative networks are built, the telephone system will remain the primary method of Internet access. It is this captive market that drives companies like US Robotics, Lucent and Rockwell to fund research into ever more complex modem technologies. With no signs, either in Europe or America, of an overhaul of the telephone network, Engineers have to squeeze every last bit-per-second out of the old analogue system. The 56 kbit/s modem represents their latest advance towards this goal.
This article is, of necessity, fairly technical. The 56 kbit/s modem is a complex device, employing advanced communications concepts. Accompanying the article is a glossary of terms, which will hopefully help to explain some of the jargon. Communications is worse than computing for its use of acronyms and abbreviations. I am happy to receive questions, either directly or through Archive, and if there is sufficient interest I will write a follow-up question and answer article. Contact details are at the end.
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