The Online World resources handbook

Getting started http://home.eunet.no/~presno/bok/v2.html
Adapters to set them apart from traditional modem technology, but from the users'
perspective, modems they are.
The recipient of data also needs a modem. In his case, the sound codes will have to
be translated back into their original form as digital codes. When this is done, he can
view text and pictures on the screen, and use the received data in other applications.
You can buy modems on an expansion card for installation in your computer, or in
a separate box. Often, a modem has already been built into the computer, when you buy
it.
Whether to buy an internal or an external modem is a question of needs:
A portable computer with an internal modem is easier to bring on travels than an
external modem with a modem cable and a power adapter.
An external modem can serve several computers. Some of them are so compact
that they fit besides your toothbrush in the toilet bag.
An internal modem blocks one of your serial ports.
External modems
The options are many. The modems differ on speed, features, prices and whether they
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Some of them are connected to the phone line by cable. Others are connected to
the handset (to the talk and listen part) by two rubber cups. We call such modems
acoustic modems (or acoustic couplers).
Acoustic modems are useful where connecting other modems to the telephone is
difficult. The bad news is that you'll get more noise on the line. Acoustic modems can
therefore not be recommended for use in other cases.
Asynchronous or synchronous modems?
Formerly, data communication was done by sending job commands to a mainframe
computer, and having the result returned in one batch. The modems were called
synchronous. Such modems (and computers) are still in use in some large corporations.
Most of today's online services are based on an interactive dialog between the user
and the remote computer. The user enters a command, for example a letter or a number
in a menu, and the result is returned almost immediately. The modems used for such
work are called asynchronous (See "Explanation of some words and terms" in Appendix
4).
Unless you know that you must have a synchronous modem, buy an asynchronous
one.
Choice of speed
Speed is measured in many ways. One method is to use baud. Another is to use
characters per second (cps) or bits per second (bps).
Bps is a measure of how many data bits that can be transferred over a data channel
in one second. (Each byte is split up into bits before transfer during serial
communication.)
The relationship between baud and bits per second is complex, and often misused.
Bits per second is unambiguous. In this book, we will use it as bps.
We can estimate the number of characters per second by dividing the number of
bps by ten. For example. 1200 bps is roughly 120 cps.
In 1987, 300, 1200 and 2400 bps asynchronous modems were the standard in many
countries. Around 1990, the growth in 9600 bps modems and modem with faster speeds
gained momentum. Today, 28000 bps modems are very popular.
Modem user manuals often give transfer speed by referring to some international
classification codes. Here are some ITU TSS codes with explanation:
V.21 0 300 bps
full duplex
Still used by a small group. Cannot
communicate with the American Bell
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