Marshall:
Thought you would like to see this commentary I just found about x2:
"Exclusive Tests Give Thumbs Down to First 56K Modems
The so-called X2 standard in U.S. Robotics's 56K modems is not ready for prime time, according to exclusive tests performed by Windows Sources. After hundreds of downloads, the best throughput achieved without using file compression was 44.8Kbps."
***** Here is the part I thought you might like to see: **********
The tests also revealed a precarious sensitivity to line noise.
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[ This sensitivity to noise is probably due to the fact that 56K uses PAM, Pulse Amplitude Modulation, which simply means that the bits are grouped into symbols, whose numeric values are transmitted as amplitudes of "pulses", or in this case, probably more like sinusoids. Unlike V.34, which also uses phase relationships in the carrier, which in turn increases the size of amplitude steps in the modulator and improves immunity to amplitude noise, 56K uses ONLY the amplitude in a finer-grained scale; it is essentially multi-level digital transmission, which is digital-like, but loses much of the noise immunity for which "digital" tranmission is famous. Line noise will thus show up as changes in amplitudes, which are translated to symbol errors, and bits errors, by the modem, which can't tell the difference between amplitude changes caused by line noise, and amplitude changes caused by the other modem. I'm not so sure we'll see the same kinds of improvements here as we've seen with V.34 between early and later releases of code; there just isn't much to "play" with here.
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remainder of story:
"And an asynchronous protocol: the faster the downlink connection, the worse the uplink speed. U.S. Robotics was first out of the chute with its 56K technology, but several competing standards are in various stages of development. Our take: We've been warning you the 56K technology is a loose cannon right now; these test results add ammunition. Don't blow your money. "
Given the price of the 56K upgrade right now, and the price of 56K modems off the shelf, although this review shows that 56K isn't 56K yet, and is touchy, I suspect that those people who are accustomed to being "unofficial beta testers" may decide that 48K is still better than 33.6K and buy the modems anyway. What the heck. I'll upgrade one of my Sportsters if any of the ISP's I can use install x2 support, which at least one has said they will do (since they host the web site for Megahertz, a local US Robotics subsidiary, you'd think they'd have gotten it done early!). I'd just like to try it out.
I guess you can't blame them for trying to wring every last bit of speed from modems; it is going to be a long dry spell before new "modems" are widely available to take us to the next level. Cable modems are disappointing in all but trial use; ADSL is going to take serious infrastructure changes before it becomes widespread; ISDN can't become much more than it is because the RBOCs don't have the capacity for it and would not spend big bucks on ISDN capacity increases when they know that the DSL's or other technologies are coming down the road --- and so forth. A lot of solutions will be tried, piecemeal, in attempts to give people the speed they crave. I wonder what the limit is for price/performance? How much would you spend to get true speed at, say, 64K over POTS? Maybe US Robotics knew that customers wouldn't spend much so they compromised on a 56K design that was focused on low cost rather then better performance?
Larry |
