Web Use Drives New 56-Kbps Standard

Downloading complex Web pages on even a 28.8-Kbps modem can exhaust anyone's patience. Help is on the way, however, in the form of modems that offer download-transmission rates of 56 Kbps. Products should start hitting the street about the time this sees print.

The so-called 56K technology is fast, but because of the nature of phone-company switching, it's asymmetrical. If there's an A/D conversion somewhere in a connection, you're limited to 33.6 Kbps. That means you get 56K only during downloads from an Internet service provider (ISP) with a direct digital connection to the Internet's main trunk lines (where ther e's only D/A conversion). Most server modems (the industrial-strength ones ISPs use at their server sites) connect to the Internet over di gital T1 lines with rates up to 1.5 Mbps.

The new 56K technology takes advantage of the digital nature of central offices by using a digital pulse code modulation (PCM) to send the data from the server to the user's modem at rates up to 56 Kbps. This encoding technology requires that a user's modem be synchronized to the network's clock rate of 8 MHz.

In brief, 56K technology uses changes in voltage amplitude to send binary data. Sampled at 8000 times per second, each sample can theoretically carry 8 bits of data, or 64 Kbps total. However, noise factors currently restrict data flow to 7 bits per second per sample, or 56 Kbps. Thus, data can flow down the standard two pairs of twisted-copper lines at the high rate in a digital form. Data flowing upstream travels at the best-possible V.34 analog speed.

For most Web users, one-way 56K isn't a bad scenario, since most of the data traffic flows from the server to the client. Mouse-clicks and the occasional text entry will fly upstream , and users could nearly double the speed of downloading pages over their present 28.8-Kbps modems.

There are other advantages as well. Modems with flash ROMs may be able to upgrade to 56K technology for a small cost. Unlike ISDN, which offers true digital transmission with two 64-Kbps channels, 56K won't require the user to install new lines or add extra-cost services. It will work just fine on existing wiring and phone connections.

But there are still some potential monkey wrenches flying about. Most have to do with that old computer-industry bugaboo, standards. Early this year, there were two principal camps pushing different approaches to 56K. On one side is U. S. Robotics (USR), with its homegrown technology supported mostly by the company and a substantial number of ISPs, supposedly those with a heavy investment in USR technology.

On the other side of the chasm stands the key player in the digital signal processor (DSP) market, Rockwell Semiconductor Systems. Allied with Rockwell are Lucent Technologies, another semiconductor giant, and Motorola, which makes semiconductors and modems. Also betting on Rockwell are most of USR's competitors in the modem market, who buy their DSPs from Rockwell, Lucent, and Motorola.

Whoever can convince the International Telecommunication Union to accept their version of 56K technology will gain a big advantage in the 56K modem marketing arena. The outcome of this battle may take most of this year, stunting the growth of this potentially useful technology. Stay tuned to the pages of BYTE to see who comes out on top.