Testing performance of sophisticated communications software on fast computers requires fast modems. As luck would have it, Microcom sent two of its DeskPorte Fast 28.8-Kbps modems as I was putting this review together. With V.42bis data compression (up to fourfold under ideal circumstances for compression), these modems are supposed to handle throughput up to 115.2 Kbps.
If you've never worked with a truly high-speed modem before (and I don't mean a 9600-bps model), you're in for a shock the first time you dial into a system and get 80- or 90-Kbps throughput on a standard voice line. Not only is that much faster than most modems can handle, it's faster than many computers can handle. The serial port on a Mac is only set to do RS-232 asynchronous communications at up to 57.6 Kbps. A PC can handle 115.2 Kbps in theory, but most systems can't because of software overload. If y
ou plan to do high-speed communications, you'll need one of the special communications boards like Hayes's ESP, or at least a serial port with a 16550 buffered UART to ease the load on the communications software.
If you're a Windows user, the problem is much more serious. Windows can't handle incoming serial streams at much over 9600 bps on most systems because of outdated 16450-type UARTs used to control the serial ports. With a newer 16550 UART you might get 19.2 Kbps, but nowhere near the speeds faster modems provide with V.42bis compression.
Microcom's solution is to put a parallel port on the modem and provide a driver that tricks your Windows communications software into thinking it's talking to a serial port. I installed the driver as COM3 on my notebook machine, and it worked exactly as advertised. Not only does the software run at full speed, but it frees up a serial port in case you're out of IRQs (interrupt request lines) on your Windows machine.
Many communications programs w
ere written before anyone even conceived of a modem running at a DTE rate of 115.2 Kbps. Procomm Plus, for example, supports only standard Hayes connect messages. When the Microcom modem reported a 28.8-Kbps connection, Procomm didn't recognize it. I had to make that connection by dialing manually or through a script I wrote in Aspect.
As another example, the BBS software we use for distributing listings is an older version of Opus running on the Fossil serial driver. Fossil had no trouble handling the high data rates, but Opus was written to expect connect speeds of up to only 38.4 Kbps. When Fossil told Opus that it had connected at a serial rate of 115.2 Kbps, Opus got hopelessly confused and assumed a 300-bps connection. The data stream was fine, but Opus overestimated transfer times by many hours. As a consequence, I wasn't able to download files much bigger than a megabyte or two without exceeding my default time limit of 1000 minutes.
When V.34, the final V.Fast standard, is approved next
spring or summer (or so people expect), don't think that you can simply buy a shiny new modem and connect it up. Your software may not understand the high-speed connect messages. You may have to replace your old nonbuffered serial ports with something better. Or perhaps you'll have to start over from scratch, as we'll have to do with our BBS. The 25-MHz 386 we normally use will barely keep up with that data rate; the serial ports certainly won't, and neither will the current software.
Should you buy a modem now? If you're equipping both ends of your data connection, there's no reason not to. All the modems available are based on the Rockwell chip set. Even though this set won't be compatible with the final standard, all the modems you can buy today are supposed to be able to talk to each other. Both Hayes and Microcom have committed to an upgrade program as well. For $39, Microcom will take back your DeskPorte and upgrade it to V.34, or send you the parts to do it yourself.
Life at 28.8
