MOBILE MODEMS
by Dale Levitt

	The average modem may as well be nailed to the desk 
where it works. I have a 14.4Kbps one that, literally, 
hasn't moved an inch since I installed it just over a year 
ago, and the only reason its three-year-old predecessor 
took the hike to the flea market was that it was terminally 
slow. I suspect that will be the fate of this one; some day 
a year or two from now I'll get tired of the leisurely pace 
at which it handles my online business, and a shiny new 
modem (five or ten times faster, at the rate the technology 
is advancing), will get its job.
	Let's face it; for computing tasks here in the 
office, any modem I use will always be a desk potato. 
	None of the conventional modems that I've ever 
owned would do my notebook computer much good. In the 
business I'm in, it's important for me to be able to write 
and send the copy where it needs to go, from wherever I am, 
so the notebook has an internal modem. Now, if I'm on the 
road as a deadline approaches, I need only to find a 
modular phone jack to make my editor happy.
	This hard-wired approach handles my data transfer 
needs very well, but for those who aren't always near 
amenities such as phone jacks, there's another way.

Modem your way out of a bind
	Suppose it's a Friday afternoon, you're on a sales 
call in a remote city, and you've just inked a sizeable 
contract with a new customer. There's no need to make this 
scenario too complex; let's just say your flight leaves in 
about an hour, you're in a rental car on the way to the 
airport, and you have to get a hard copy of the order to 
your sales department before the weekend. It could happen, 
right?
	For this situation, it's useless to search for a 
modular jack. There's no time. What you need is a cellular 
modem.
	That's right; a cellular modem. It's exactly what 
it sounds like. One configuration uses an adapter to 
connect an external battery-powered modem with a cellular 
phone, for the transmission of data instead of voice 
messages. It does its job well, under most conditions. 
	Another method is to add cellular features 
directly to your computer's internal modem.
	The big problem is inconsistency. Like cellular 
voice coverage, especially while you're moving, dropouts 
occur even where most cellular performance is fine.

Sneaking in the packet
	Another approach to cellular data transmission 
is the use of technology like that of packet radio. In 
this case, the data uses the same frequencies as regular 
cellular customers, but instead of a separate 
transmission, it's sent in bursts during the idle time 
between calls. These unused periods, five to ten seconds 
long after the end of a cellular call, leave time for the 
transmission of ten or more kilobytes of data in packets 
of 256 bytes before another voice call can use the 
channel. The packet data gets a free ride, and there's no 
congestion of cellular channels.
	Future opportunities for the use of modems for 
wireless data transmission can only get brighter, as 
direct-to-satellite and other technologies come on line.
	Over forty years ago, cartoonist Chester Gould 
gave Dick Tracy, his square-jawed detective hero, wrist-
mounted audio-video electronics with no range limits. 
	After all this time, we may soon match the 
technological sophistication of a 1950s comic strip.

		       Copyright 1995 SeeJay Publications