Programmer 7500/MAX_PROGRAMMERS.iso/PROGRAMS/UTILS/DOS_HELP/PCLEARN.ZIP/MODEM.TUT

Text File | 1988-12-13 | 12.8 KB | 224 lines

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THE JOY OF MODEMS - THE FRUSTRATION IS WORTH THE EFFORT!
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Two concepts best summarize computer/modem telecommunications: addiction
and mild frustration.

Put simply, modem communication is perhaps the most addictive, useful and
powerful application of a computer - albeit a process fraught with the
need for patience and persistence. No pain, no gain, as they say. First
let's look at the pieces the puzzle . . .

Computer telecommunications, simply stated, is the process of hooking one
(or more) computers together via a telephone line to exchange files of
information and  programs or carry on a live conversation. Your computer
will need a device called a modem which allows data to be converted into a
special signal which can be transmitted over phone lines to another
computer which awaits the information.

There are two types of modems: internal and external. External modems are
slightly more expensive than internal modems and are housed in an external
box or enclosure. External modems require a socket on the computer or port
(usually the serial port on the back of your computer.) The serial port is
also called a com port, com for communications. Most PC's come with a
serial port, a few must have it installed. If you are already using the
serial port for something else (e.g., a mouse or pointing device) you may
need an additional port installed or temporarily unplug the device using
the serial port. External modems take up a bit more space and add a bit
more clutter (internal modems mount inside the computer.) However some
people like the external modem with its blinking lights which instantly
displays call status - something a hidden internal modem cannot do unless
special display software is also installed or activated. Another
consideration is that external modems are portable, you can move from
machine to machine by simply unplugging the external modem and taking it
home or to the next job site.

Next some basic terminology to help things along. The "host computer"
refers to the computer your pc is calling. Sometimes this is a commercial
service such as The Source or Compuserve which are large interactive
computers. Other times the host may be another pc your friend is using on
the other side of town or perhaps a BBS (bulletin board system) which is a
computer operated for general public access by a private individual or
company with files and messages of general public interest and access.
Another important term is the baud rate associated with the modem
transmission process. Essentially baud is a reference to the speed at
which your modem and the host modem exchange information. Some common
rates are 300 baud, 1200 baud and 2400 baud. A 1200 baud modem is roughly
4 times faster than a 300 baud modem. And since you may be transmitting
information via long distance lines, speed and brevity of the modem link
is of interest. Some BBS (bulletin board systems) will not allow slower
300 baud modems to load or access software files since this ties up the
board for other users. As an aside, a 2400 baud modem can be switched to
transmit and receive at the slower 1200 and 300 baud rates so there is
some "downward" flexibility in purchasing a high speed modem which allows
lower baud rates as needed.

Curiously the software which controls the modem and computers linking
during this exchange will "synchronize" the two modems, determine which
modem is using the slower speed and adjust the faster modem downward to a
slower speed. Many BBS systems use the 2400 baud rate and some are even
capable of 9600 baud - in this case the BBS host computer will slow to
your rate. If you plan to do much long distance modem work, the 2400 baud
modem is the wiser choice at a somewhat higher initial purchase price
which will obviously be offset by savings in reduced long distance rates.

Next we dip into the software pool. While DOS controls the internal
workings of your computer, you'll need communications software (sometimes
called terminal software) to enable the pc, modem and telephone line to
work together. Many commercial software packages have a communications
package built in or added as a separate module. Shareware and public
domain packages also exist (which are themselves obtained from BBS systems
via modem!).

The baffling part of the software setup process is configuring the
software package to your pc and modem. The software needs to be told if
you are using serial port (com port) one or two. You will need to tell the
communications software which directory or drive where files will
be sent or downloaded. The baud rate must be set as well as noting if the
modem is hayes compatible (Hayes compatibility refers to a standard set of
transmission instructions which many modems share.)

The modem software must also be told other seemingly obscure details
such as parity, and data bits. Generally data bits are set to 8. Parity is
usually set to no. Commercial services such Compuserve offer exception to
these settings and will tell you these settings in their literature.

An example: If parity is required, set data bits to 7. Set stop bit to 1.
The eighth bit is usually then used to check parity/accuracy. Thus the
above setting is somewhat cryptically referred to as 8N1 which means 8
bits, no parity, one stop bit. Don't worry about this too much now -
frequently this is a one time setup which you don't have to fiddle with
once the software has been set.

Other settings can include ANSI standard terminal emulation (a standard
selection you should check if given the choice). ANSI terminal emulation
is usually the default setting and should only rarely be changed.

Protocols must also be specified. In simplest terms a protocol is a
method of checking for errors between modems as the data transmission
progresses. In a precise fashion, these protocols tell the first
modem to transmit data for a short time then the receiving modem will play
back that short piece of the entire message. The transmitting modem stops,
listens for a time and if the short piece matches the information which
it sent, the first modem then transmits the next piece of the main
message. This continues on and on, one small chunk of data at a time.

Uploading data to the host (you transmit data to the other computer)
and downloading data (you receive data from the other computer) requires
selection of a protocol. Several common protocols include Xmodem,
Ymodem, Xmodem-CRC, Zmodem. Xmodem is generally offered by most BBS
systems and is a safe bet if you are not sure. Other protocols
are somewhat faster and/or slightly more dependable, but Xmodem
will usually do the job. Trial and error or simply logging onto the
BBS system with Xmodem and then inspecting the menu of other protocols
available (one logged on) will give you more detailed information.

Many shareware modem/communications packages are available (and can
obviously be obtained directly from BBS systems.) Some of the more
dependable packages include Qmodem, Procomm, Boyan, Telix, and
GTpowercom. Good communications software is flexible and powerful
without being difficult to start and use. The best have help
screens and tutorials as with many software packages in general.
Some general considerations in selecting a software package
for modem use include:

* The dialing directory is of crucial importance. The idea is that
the package will store and dial your most frequently dialed numbers.
Some packages hold only a few, some quite a lot! Does the package
store your individual password and comments next to each number?
You may wish to use different passwords for each BBS system you call,
a flexible and complete dialing listing becomes essential.

* Consideration of transfer protocols offered. Xmodem is a basic, but
you may want more efficient protocols later. Make sure the package
supports several or can be upgraded to more protocols later.

* How does the package dial numbers from the list? Will it call back and
continue trying? Can it dial numbers from the list in a certain order.
Can it do circular dialing (several numbers are called in a row, then
the program jumps from the bottom of the list and starts at the
beginning again - around and around in a circle)?  This sort of
redialing efficiency is important if you deal with busy communmications
services and BBS systems where it may take time and several attempts
to log on to a system especially during the busy evening peak time.


* Does the package offer scripts? Simply stated a script is a way of
having the package automate several steps. Without further input
the package can call a BBS system, type in your password and then
continue typing further keystrokes as if you were entering them
from the keyboard yourself - in essence a script capability is a
programming-like language that gives the communications software
package a customized way to enter many keystrokes while you only
input one or two strokes to start the chain reaction. Many programs
let you even record the sequence of keystrokes during a communications
session for playback and retrieval later. Beware though, if the
system which you are calling changes log on sequences you may have to
go back and later revise your original script - not a major problem, just
a concern to be be aware of.

* Is it possible to capture screen information to your disk drive?
Can you output screen information to hour printer? Long communication
sessions on line with your modem produce endless screens of information
which scroll by quickly. The ability of your software package to output
all or selected parts of your session to permanent disc or printer
output can be a tidy bonus.

BBS systems can offer the most entertainment and information for the
first time user. The cardinal rule of behavior: "act as if you are
in someone else's home." Courteous behavior is a must.

Most BBS systems will allow you to tour within the various activities
and parts of the system for 30 minutes to an hour on your first call.
After that you are expected by some "boards" to leave your name and a
phone number where you can be reached for verification. Some boards
are free, some request a nominal use fee (usually around $25 per year.)
Some boards request that you upload (send to them via modem) shareware
files or public domain software in order to download their software.
After a while the process is a bit like two kids with bubble gum trading
cards: "I'll trade you 125,000 bytes of this file for 200,000 bytes
of your files."

On your first visit into a BBS board you usually are allowed access only
to certain "low level" but nonetheless interesting areas of the board.
The SYSOP (system operator) may be available to come "online" if you
experience difficulty. You the software of the BBS system itself will
safely keep you from damaging the host computer even if you hit an incorrect
key or enter an erroneous command. You can leave messages for the SYSOP,
leave messages of a general nature, ask for help on a specific question,
download public domain software, play a game, or just generally explore
the information within the system of the host computer. Downloading files
is easy, generally for many boards the command is a simple "D" for
download. The BBS will ask you the name of the file you wish to download
and then give you an estimate of how long it will take and the modem
protocol you will (or should!) be using. After that you key in a
keystroke or combination which tells your software in your computer
to begin the process. When the transfer is complete, the host BBS takes over
and presents a menu of choices or selections you wish to do - in essence
you can continue to browse as before.

Lists of phone numbers for online services and BBS numbers are available
from the boards themselves and many local newsletters of computer clubs
and many computer store salespersons.

Most public domain and shareware software from BBS systems is stored and
transmitted in a compacted form called an archive or ARC for short.
You will need a small public domain program (PKARC, ARC or NARC) also
available from the BBS board to unpack the software. This archiving
or "arcing" process is done to compact the software for shorter, more
efficient transmission - it saves time and disk space for both the
BBS host computer and your computer.

Working with modems and telecommunications software sounds arcane and
a bit daunting at first, but it is a thoroughly enjoyable and rewarding
pastime - and also a nice way to make friends and delve deeper into
the global network of information and friendships this new form
of communication represents.



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