ps modems, we measured around only an 8 percent gain. It's not enough to justify upgrading from 28.8 Kbps, but it's the best route for upgrading from 14.4 Kbps, particularly if ISDN isn't an option.
While we were testing the first crop of 33.6-Kbps modems, vendors were already announcing so-called 56K modems (see the article "Web Use Drives New 56-Kbps Standard"). Capable of download rates of 56 Kbps, these devices could supplant 33.6-Kbps modems fairly quickly.
That shouldn't necessarily stop you from buying a 33.6-Kbps modem now, however; most vendors are just announcing policies for inexpensively upgrading 28.8- and 33.6
-Kbps modems to a proprietary 56K capability. Once the ITU settles on a 56K standard, a final upgrade will be available for free from most vendors.
We tested 13 of the first enhanced V.34 modems. All are external models that you can use on several hardware platforms, although the test units all came with Windows software.
It's a varied lot, ranging in price from $109 for the modest Practical Peripherals PM336MT INET to $395 for Digicom Systems' ScoutPro and the U.S. Robotics Courier V.Everything/V.34. Eight vendors sent models offering some voice-messaging and/or speakerphone capabilities, although that wasn't a requirement for participation. Six of the modems offer flash ROM BIOS chips that allow you to upgrade the device using a vendor-supplied program.
Our review doesn't include internal versions of 33.6-Kbps modems. Since they generally use the same data pumps and chip sets as their external cousins, the performance differences are minimal. Cost differentials are generally minimal as well; the
average difference is about $20. All these products include fax capabilities at the highest standard rate (V.17) of 14.4 Kbps. We did not test fax performance, as previous tests have shown virtually no speed differentials.
Speed Is Important
What must you know before making a decision about which model to buy? Speed is, of course, critical. We found a noticeable 15 percent difference between the fastest and slowest modems in our testing. And, as with 28.8-Kbps modems, there are several factors that can prevent you from using full V.34 speed.
First, you must connect to another V.34 modem. For companies supporting telecommuters, that means upgrading existing installations, and Web users must wait for their ISPs to upgrade their modem banks. A few older V.34 modems have programmable BIOS chips (flash ROM or EEPROM), which can be upgraded to the latest V.34 standard.
A second limiting factor is the quality of your phone lines. The number of lines that are "clean" enough for 33.6-
Kbps transmission in the U.S. is estimated at 5 percent. However, the new V.34 specification also enhances a modem's transmission abilities on more-typical phone lines. So, even with less-than-perfect lines, a 33.6-Kbps modem will give you higher throughput than an older 28.8-Kbps model.
A third possible limitation is your computer's serial port. Modems compress data before transmitting it. To transmit compressed data at a 33.6-Kbps data communications equipment (DCE) rate, uncompressed data must flow into the modem at an even-higher data terminal equipment (DTE) rate. At the highest V.42bis compression ratio (a seldom-reached 4:1), the serial port must transmit at 115.2 Kbps. Few serial ports on older systems can handle this rate, or even 56.6 Kbps. (This isn't a problem with internal modems, because data comes off the expansion bus.) In either case, a 16550-compatible universal asynchronous receiver/transmitter (UART) is another requirement for fast data flow.
In addition to speed, another desirable
feature is a flash ROM BIOS chip and/or EEPROM. Since most modern modems use DSPs (digital signal processors), vendors can upgrade the operation of the DSP using a reprogrammable BIOS chip. That way, they can add features, improve compatibility, or upgrade to new standards without having to open the modem.
A speakerphone function is important for telecommuters and home-office users. While some modems have built-in speakers and microphones, some buyers might also want to be able to connect a modem directly to their computer's sound card or even use a headset.
Key features for home-office users are support for caller ID and distinctive ringing. Caller ID lets you identify a caller's phone number before picking up. Eight modems in this review offer this feature. (Note: Bundled software doesn't always support caller ID.) Distinctive ringing is a telco service that allows several different phone numbers to use the same line. You can, for instance, dedicate one number to voice calls and a second to fax and
data calls and then configure the modem to answer one ring and not the other -- if the modem supports distinctive ringing.
We rated the modems primarily on their speed (which constitutes 40 percent of the total score). NSTL's speed tests look at transmission rates under normal line conditions (representing half the calls made in the U.S.); under heavily impaired conditions (the most stressful, but rarely encountered); and under the conditions specified by the TIA standards body, which represent more than 90 percent of all the calls made in the U.S. We also rated the products for feature sets and usability.
While we didn't include bundled communications software in the ratings (see the article "Software: Bundle or Burden?"), we installed each package to get a feel for its form and function. All modems with voice features also had software for setting up voice mailboxes; most also offered fax-back functions as well.
Contributors
Kathleen Bishop,
analyst/NSTL
Mary Anne Eves
, acquisition specialist/NSTL
Andrew Froning,
managing editor/NSTL
Helen Holzbaur,
telecommunications test manager/NSTL
Dorothy Hudson,
project manager/NSTL
Dave Rowell,
senior technical editor/BYTE
illustration_link (78 Kbytes)
13 Modems: Fast for the Web
