In initial tests of 56k-bps modems, PC Week Labs had difficulty connecting at the advertised throughput rate. In further tests, we managed to connect at these higher data rates, using modems from U.S. Robotics Corp., but we aren't changing our original recommendation: Make sure these modems will work from a given location before buying.
In tests performed by PC Week Labs and sister publications Windows Sources and PC Magazine, connecting at 56K bps with the U.S. Robotics $395 Courier V.Everything x2 modem and $219 Sportster 56K Faxmodem was limited more by phone line infrastructure problems than any fault of the modems. At any rate, the results were discouraging: We could connect at 56K bps only from about 55 percent of the locations we tried.
There are a few factors corporate buyers should consider before buying into the technology. First, the modems require a special switch at the point of service, instead of another modem. In our tests, we dialed in to a U.S. Robotics Total Control NetServer/8 I-modem switch at a U.S. Robotics site and at Windows Sources offices. Firms will need to buy either a similar switch to set up a modem pool or connect via an Internet service provider with one of these switches.
According to U.S. Robotics officials, the 56K-bps modems should work with 90 percent to 95 percent of phone lines. However, the analog-to-digital conversion that occurs at a PBX reduces throughput. For corporate applications, this means remote users dialing through a PBX (from a hotel or remote office, for example) are less likely than users telecommuting from their homes to see a high-speed connection.
When dialing in from residences in Boston, Florida, New York and Pennsylvania, we could connect to the U.S. Robotics and Windows Sources sites at data rates between 44K bps and 52K bps. When we dialed out through a PBX, we generally got a connection at 28.8K-bps or 33.6K-bps speeds.
Line quality also plays a role in the modems' performance. When dialing from two lines in an apartment in Boston, we saw connection rates ranging from 19.2K to 48K bps; using the apartment's older line, connection rates ranged from 44K to 48K bps, but we couldn't connect at higher rates than 19.2K bps using a recently installed second line.
The new 56K-bps modems have asymmetrical data rates, with the downstream rate being greater than the upstream rate, making them better suited for Web browsing rather than applications such as videoconferencing that require symmetrical data rates.
The Courier modem has flash memory, so it can be upgraded to support emerging standards. U.S. Robotics is offering a $60 flash upgrade to 56.6K-bps speeds for its 33.6K-bps Courier.