Double Trouble for 56-Kbps Modems

Real-world limitations and questions of compatibility lurk beneath emerging 56-Kbps modem technologies.

Dave Andrews

New modem technology promises to let you surf the Internet almost twice as fast as you can with current 33.6-Kbps analog modems, but in some cases your connection won't be any faster than the fastest you get today. And it appears that the market may have to sort out incompatibility problems.

The 56-Kbps modem technologies, such as the one from Rockwell Semiconductor Systems, take advantage of the Public Switched Telephone Network's (PSTN's) shift toward becoming a digital network. Now that many Internet service providers (ISPs) and corporations connect to the Internet over high-speed digital (e.g., T1) lines, the only analog portion of a conn ection occurs over the copper wire that's between your home or office and the local phone company's central office. Yet current modems treat the entire PSTN as an analog system.

Due to distortion that impedes the pulse-code-modulation process, analog-to-analog communications top out at 33.6 Kbps. But when the only analog portion of a communications session is the local loop, you can theoretically send 64 Kbps from ISP to end user without having to upgrade the local phone company's equipment, as you do with ISDN.

But one problem with this technique is that a number of factors, including problems with equalization and overhead in T1 lines (e.g., robbed bit signaling), reduce the theoretical maximum that you can achieve to 56 Kbps from the ISP or corporation to the home and just 30 Kbps from the home back to new central-site modems (which will also need to be upgraded). ISPs must have a digital connection to the network, and Rockwell's scheme will not tolerate any digital conv ersions on the network, such as those that take place in U.S.-to-Europe communications. With such conversion, the connection bit rate backs down to today's slower speeds.

A second problem: standards. Several modem companies will release fast modems based on Rockwell's technology. And Rockwell says it will submit its technology to international standards bodies. But Paul Kraska of modem vendor Multi-Tech says that releasing prestandard modems is "horribly immature."

Other companies, such as Lucent Technologies, U.S. Robotics, and Motorola, are working on similar, but not identical, technologies. Those companies also say they will submit their technology to standards committees. But with modems slated to arrive in 1997, possibly a year before the final standard, the industry may find itself once again staring at a slew of modems that don't work with each other. Multi-Tech will introduce a 56-Kbps modem at Comdex, based on Lucent technology. But Kraska adds that the company will do so reluctantly. "If ou r competitors introduce 56-Kbps modems, we have to as well," he says. "We can't afford not to."