There is one hard limit, the analog line gets converted into a digital one with 256 levels and 8000 samples per second, thus 64,000 bits per second (not 64k) is all there is.
Re:Lady, there ain't nothin' so complicated...
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A Brief History of Modems
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· Score: 2, Interesting
You are somewhat understating the complexity of the 24-33k modems. Not only do they have high-level QAM modulations but there's probably the most sophisticated error correction coding in there out of any commercial products, even now. This was largely because the computing power was available (the input was only 8,000 samples per second) and the market would pay for it. There were lots of PhD theses and lots of patents involved in those designs. In contrast the 56k "modems" really just encode 256 levels per 1/8000 of a second (having to adapt to voltage gains and nonlinearities in the phone line make this far from trivial but it's intrinsically pretty simple).
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There is one hard limit, the analog line gets converted into a digital one with 256 levels and 8000 samples per second, thus 64,000 bits per second (not 64k) is all there is.
You are somewhat understating the complexity of the 24-33k modems. Not only do they have high-level QAM modulations but there's probably the most sophisticated error correction coding in there out of any commercial products, even now. This was largely because the computing power was available (the input was only 8,000 samples per second) and the market would pay for it. There were lots of PhD theses and lots of patents involved in those designs. In contrast the 56k "modems" really just encode 256 levels per 1/8000 of a second (having to adapt to voltage gains and nonlinearities in the phone line make this far from trivial but it's intrinsically pretty simple).