Help-desk: 28.8kbit/s modems not obsolete

Fear not, the latest modem standard does not render your V.34 device entirely obsolete.

Q: A business associate just purchased a modem that he claims can achieve data rates of 33.6kbit/s. I thought V.34 modems -- with a maximum data rate of 28.8kbit/s -- were the fastest that were going to exist and so bought a bunch of them for my company. What gives? Are our modems obsolete again?

A: No, but there are still good reasons to buy the more capable modems in the future. Given the normal bandwidth of a phone line, the theoretical maximum speed of an analogue modem is about 35kbit/s -- if conditions are just about perfect. And 28.8kbit/s is about the best you can hope for on anything but a call to a destination served by the same central office. But because it's possible to eke out just a bit more speed on interoffice calls within the same city or calls to local Internet service providers, the International Telecommunications Union (ITU) is about to ratify an enhanced version of the V.34 standard: ITU-T V.34 Annex 12. It attains faster speeds by adding one more point to the phase/amplitude "constellation" of a V.34 modem.

Why should you care about buying a modem that runs at a speed that can seldom be attained? Because it won't offer just a 17% speedup under ideal conditions, it'll also have one intermediate speed (31.2kbit/s) and be more noise-resistant at lower speeds. Thus, it pays to insist upon a 33.6kbit/s unit even if you don't expect it to run at full bore all the time. If you have a V.34 modem now, you may be able to upgrade it. Sophisticated modems based on digital signal processors (DSPs) will be capable of handling the new baud rates if you "flash" the ROMs. Less expensive units based on hard-wire chip sets won't.

Capabilities may vary even among different models made by the same vendor. Multi-Tech Systems' high-end commercial modems, such as the MT2834BA, have 33.6kbit/s capabilities, and older ones will accept a flash upgrade (available now from Multi-Tech's Web site). However, all but one of its low-cost ZDX models, based on an AT&T chip set, will not. Supra claims that its new SupraSonic modem will be upgradable to the new standard sometime in the future, but owners of its SupraFaxModem 28.8, based on a bargain-price Rockwell International chip set, are out of luck. US Robotics, which has used DSPs in most of its modems for many years, is a strong supporter of the new standard. To find out if your modem is upgradable, go to Curt's High Speed Modem Page ( and follow the link to your vendor's home page. As a bonus, this page has one of the best FAQs (lists of frequently asked questions) about modems on the World Wide Web.

(Brett Glass' Help-desk answers business computing questions. To submit a query, send email to

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