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MODEM
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1991-02-20
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Perhaps two notions best describe computer/modem telecommunications:
┌───────────┐
░│ │
░│ Addiction │
░│ ┌───────┴──────────┐
░└───┤ │
░░░░░│ Mild frustration │
░│ │
░└──────────────────┘
░░░░░░░░░░░░░░░░░░░ ███████████
█▄▄▄▄▄▄▄▄▄█░
Did you say... ██░░░░░░░██░
██░MILD?░██░
██░░░░░░░██░
█▀▀▀▀▀▀▀▀▀█░
███████████░
░░░░░░░░░░░
Modem communication can be the most addictive, useful, and powerful applica-
tion of a computer. It's a process loaded with the need for patience and
persistence. However, "No pain, no gain!"
Computer telecommunications is the process of hooking two computers together
through a telephone line to exchange files of information and programs or
carry on live conversations. Your computer will need a device called a MODEM
which allows data to be converted into a special signal which can be trans-
mitted over a phone line to another computer.
There are two types of modems:
┌──────────┐ ┌──────────┐
│ Internal │ and │ External │
└──────────┘ └──────────┘
External modems are a bit more expensive than internal modems because they
have their own case and power supply. 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. <RS232>
If you are already using the serial port for something else like a mouse or
joy stick) you may need an additional port installed. You may be able to
temporarily unplug the device using the serial port. External modems take up
a bit more space and add a bit more clutter on your desk (internal modems are
installed inside the computer.) Some people like the external modem with its
blinking lights which instantly displays the call status. Another consider-
ation is that external modems are portable and can be moved from machine to
machine by simply unplugging the modem.
DEFINITIONS
The "host computer" is the one your PC is calling. Sometimes this is a
commercial service such as Delphi, GEnie, Prodigy, or Compuserve which are
large interactive services. Other times the host may be another PC your
friend is using on the other side of town or perhaps a bulletin board system
(BBS) 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 baud rate. It is associated with the modem trans-
mission process. 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. You should obtain the fastest baud rate modem you can afford.
Most BBS systems will not even let you connect at 300 baud any more.
A 1200 baud modem is roughly 4 times faster than a 300 baud modem. Since you
may be transmitting information long distances, speed, and brevity of the
modem link can really be an important factor.
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.
The software which controls the modems, and computers linking during the
exchange will "synchronize" the two modems, determine which modem is using the
slower speed and adjust the faster modem downward to that speed. Many BBS
systems use the 2400 baud rate and some are even capable of 9600, 14,400, or
even 38,800 baud - in this case the BBS host computer will slow to your rate.
If you plan to do much long distance modem work, a 2400 baud modem, or faster,
is the wisest choice. The higher purchase price which will be offset by
savings in reduced long distance rates.
Next, take a look at the communications software. While DOS controls the
internal workings of your computer, you'll need communications software to
enable the PC, modem, and telephone line to work together. Many "integrated"
commercial software packages have a communications package built in or added
as a separate module.
Shareware and public domain packages also exist. Some of the more dependable
software packages include:
░░░░░░░░░░░
┌────────┐░
│ │░
│ Qmodem │░░░░░░
│ ├────┐░
└───┬────┘ │░
│ Procomm │░░░░
│ ├──┐░
└────┬────┘ │░
│ Boyan │░░░░░
│ ╞═══╗░
└───╥───┘ ║░
║ Telix ║░
║ ║░
╚═══════╝ ░░░░░░░
┌─────┐░
│ and │░ ░░░░░░░░░░░░░░░░
└─────┘ ┌──────────────┐░
│ │░
│ GTPowercomm │░
│ │
└──────────────┘
Good communications software is flexible and powerful without being hard to
use. The best comm programs have help screens and tutorials. Telix, for
example asks a few simple setup questions then attempts to set the numerical
settings needed without operator intervention or frustration.
Here at MICRONEWS, Telix is the communications package of choice.
Although obscure at first, the modem software setup process allows you to
configure the software package for your specific PC and modem combination.
The modem software needs to be told which serial port (COM port...usually 1 or
2) you will be using.
You will need to tell the software which directory or drive where files will
be sent (downloaded). The baud rate must be set. You will usually have to
tell if the modem is Hayes compatible. Hayes compatibility refers to a
standard set of transmission instructions which many modems share.
Other basic details like <PAR>ITY, and DATA BITS have to be set. These refer
to how the data is "grouped or packaged" during the actual modem transmission.
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.
This is a total of 1 + 7 = 8 Bits. The final bit is usually
used to check parity/accuracy. The above setting is cryptical-
ly referred to as 8N1 which means 8 bits, no parity, one stop
bit. Don't worry about this too much. Often this is a one
time setup. Once its done you can forget it.
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 will have to be specified. The 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 a small packet of
data . . . then the receiving modem will play back a short verifcation
"checksum" or "password." The transmitting modem stops, listens for the
checksum and if it matches the information which was sent, the first modem
transmits the next packet of the message. This continues, one small packet of
information/data at a time. The idea is to protect data integrity over noisy,
static-prone telephone lines.
You need a protocol for sending (up;oading) or receiving (downloading) data.
Several common protocols include Xmodem, Ymodem, Xmodem-CRC, and Zmodem.
Xmodem is generally offered by most BBS systems and is a safe bet when you are
not sure what to use. Other protocols are somewhat faster and/or slightly
more dependable, but Xmodem will do the job. Trial and error or simply
logging onto the BBS system with Xmodem and then inspecting the menu of other
protocols available will give you more detailed information and clues about
other possible protocols.
Ymodem offers a faster transmission rate than Xmodem, better data security
through a refined CRC checksum method and finally a method for "batching" or
sending/receiving several files one after another unattended.
Zmodem is faster still, somewhat more secure with respect to data loss,
likewise offers batch transmission of many files and additionally allows a
file to be partially stored if the connection is lost and then completed when
the connection is restablished so you do not have to transmit the entire file
again!
General considerations in selecting software for modem use include:
* The dialing directory is REALLY important. 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? What about linked scripts
that will run whenever a specific online connection is made? You may
wish to use different passwords for each BBS system you call.
* 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. Zmodem one is the best.
* How are numbers dialed from the list? Will the program call back and
continue trying if the number is busy? 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
type of dialing is important if you deal with busy communications
services and BBS systems where it may take time and several calling
attempts before logging on to a system especially during the busy evening
peak time.
* Does the package offer scripts or macros? 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 name and password and then continue
typing further keystrokes as if you were entering them from the keyboard
yourself. Script capability is a programming-like language which gives
the communications software package a customized way to enter many
keystrokes while you only input one or two strokes to start the process.
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, but sometimes it can be a hassle.
* Does the program allow you to capture screen information to your disk
drive? Can you send screen information to your printer? Long communica-
tion sessions on line with your modem produce endless screens of informa-
tion which scroll by quickly. The ability of your software package to
output all or selected parts of your session to permanent disk file or
printer output can be a definite bonus.
Local neighborhood BBS systems can offer the most entertainment and informa-
tion for the first time user. The principal rule of behavior: "Act like you
are in a good freind's home." Courteous behavior is a must. How do you find
telephone numbers for these systems? Consult local computer clubs for a few
numbers for BBS systems and then call the BBS systems with your modem for
lists of MORE local telephone numbers. BBS operators and users are quick to
answer questions for new users and can serve as helpful "experts" on any
computer question. Operators of these BBS systems are frequently called
Sysops and many provide BBS systems as a hobby activity much as other hobby-
ists enjoy short wave radio operation.
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. The process is something like two kids with
baseball trading cards: "I'll trade you 225,000 bytes of this shareware file
for 250,000 bytes of your files."
You usually are allowed access only to certain "low level" (but interesting)
areas of the BBS "board" on your first visit. The Sysop (system operator) may
be available to come "online" if you experience difficulty. 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 a wrong command. You may 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. 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 the software in your computer to begin the process. When the
transfer is complete, the host BBS takes over and presents the main menu of
choices or selections.
Lists of phone numbers for online services and BBS numbers are available from
most of the boards themselves, local computer club newsletters, 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 (ARC, ZIP. PAK, or LZH
format). You will need a small public domain or shareware program also
available from the BBS board to unarchive (unpack) the software. This archiv-
ing process is done to compact the software for shorter, more efficient
transmission. It saves time and disk space for both the BBS and you. The
easiest way to visualize arc'd or zip'd software is to think of the many files
of a typical software package compacted in size and then placed into one
single file. You might also wish to compact your other files for storage on a
hard drive aside from the modem process. File compaction is a useful tool all
by itself! PKARC, PKZIP, PAK, and LHARC software are shareware packages
available from BBS systems.
Working with modems and telecommunications software sounds mysterious and
intimidating at first. However, it is a thoroughly enjoyable and rewarding
hobby. It's also a nice way to make friends and explore more deeply the
global network of information and friendships.
MICRONEWS...
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