| You must have a computer.
It is not important what kind of computer you have, though you may find out
that it is an advantage to have a popular one. The most common type of
microcomputer today is called MS-DOS computers (or IBM PC compatibles or
IBM clones).
 Your computer should have
enough memory for communication. Available memory impacts communications
speed on many modern computers!
You do not need a hard disk.
Many do without. Not having one, however, means more work, and less room
for storage of the nice things you may want to retrieve by modem.
Personally, I want as much
hard disk space as I can possibly get. When you have read the book, I guess
you'll understand why.
Others may want to delay the
purchase of a hard disk until they can spare the money. If you can afford
it, however, do it! It is a decision that you'll never regret.
You must have a modem
Some computers are always connected to a network. If this is your situation,
then you probably have what you need already. The rest of us need a modem.
A modem is a small piece of
equipment that is translating the internal, electrical signals of the computer
to sound codes. These codes can be sent over an ordinary telephone line.
You may think of it as a type of Morse alphabet.
In some places, a computer
can be connected to the Internet and other networks through cable television
networks. Cable modems use the same lines that transmit cable television
to provide two-way telecommunications.
There are also ISDN and ASDL
modems. Sometimes these are called Terminal 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 are approved for usage in your country.
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
103 standard. |
| V.22 |
|
1200 bps
full duplex |
|
Partly compatible with the American Bell 212a standard. Sometimes it
works, sometimes it fails. |
| V.22bis |
|
2400 bps
full duplex |
|
Used all over the world. |
| V.23 |
|
600 & 1200
bps w/75
bps return ch. |
|
Rare protocol. Used mainly in Europe. Half duplex. |
| V.26ter |
|
2400 bps
full duplex |
|
Used mainly in France |
| V.27ter |
|
2400/4800 bps
half duplex |
|
Used in Group III fax |
| V.29 |
|
4800, 7200 and
9600 bps
half duplex |
|
Used in gr. III fax and in some (American) modems. Do not buy V.29 if
you want a 9600 bps modem. |
| V.32 |
|
4800/9600 bps
full duplex |
|
Current standard for 9600 bps modems |
| V.32bis |
|
4800/7200/9600,
12000/14400 bps |
|
Full duplex with faster interrogation. |
| V.Fast also known asV.32terbo V.FC |
|
28800 bps |
|
Proprietary protocols supporting speeds to 28,800 bps for uncompressed
(raw) data transmission rates over regular dial- up, voice-grade lines. Using
V.42bis data compression, up to 86,400 bps may be achievable. Some claim
throughput of up to 115.2 kbps with V.42bis compression. Incompatibility
between brands. |
| V.34 |
|
28800 bps |
|
A standard high speed protocol approved by ITU-TSS (1994). |
| V.34bis |
|
33.6 Kbit/sec |
|
|
| V.42 |
|
|
|
Error correction protocol (an appendix yields compatibility w/MNP gr.
2,3 and 4. See MNP below). For V.22, V.22bis, V.26ter and V.32. |
| V.42bis |
|
|
|
Data compression for V.42 modems. Meant to replace MNP and LAP. Text
can be transferred three times faster than with MNP. With a 9600 bps modem,
you may achieve speeds of up to 38400 bps. Very common. |
| V.90 |
|
56 Kbits/sec |
|
Receives up to 56.000 bits/s over ordinary telephone lines, sends at
33.600 bits/s. Still under development. Proprietary systems. Both you and
your online service provider must be connected to a digital line. Two types:
2x modems, and K56flex modems. |
| ?? |
|
112 Kbits/sec |
|
Boca Research Inc. was the first to announce such a modem (November 1997). |
When you consider buying a modem with higher speed, remember that going from
1200 bps to 2400 is a 50 percent increase, while going from 1200 to 9600
bps gives 800 percent!
If you now have 9600 bits/s,
going to 28.800 will potentially triple the speed.
MNP error correction and compression
The Microcom Networking Protocol (MNP) is a U.S. industry standard for
modem-to-modem communication with automatic error correction and compression.
Automatic error correction
is useful when there is noise on the telephone line. MNP splits the stream
of data up into blocks before transmission. They are checked by the other
modem upon receipt. If the contents are correct, an acknowledging message
is sent back to the sending modem. If there is an error in the transmission,
the sending modem is asked to retransmit.
When using compression, files
are being preprocessed before transmission to decrease their size. The result
is that the modem has to send fewer bytes, and the effect is higher speed.
MNP Level 3 and up send data
between two modems synchronously rather than asynchronously. Since sending
a start and stop bit with each transferred byte is no longer required, the
effect is higher speed.
MNP-4 or higher have automatic
adjustment of block length when there is noise on the line. If the line is
good, longer blocks are sent. The block size is decreased if the line is
bad causing many retransmissions.
MNP-5 has data compression.
This gives a further increase in transfer speed by from 10 to 80 percent
depending on the type of data sent. MNP-7 is capable of a three-to-one
compression ratio.
Both users must have their
modems set for MNP to use it.
The speed of your computer's COMM port
Installing a super fast modem does not guarantee an increase in the effective
transfer speed. The serial port of your computer may be a limiting factor.
Owners of older MS-DOS computers
often have UARTs (serial port processors) in the Intel 8250 or National 16450
series. With these in the computer, it is difficult to achieve speeds above
9600 bps without losing data.
Take this into account when
investing in a modem.
MNP and efficiency
I call the Internet daily. My personal computer is set to communicate with
a 28.800 bps modem at 57.600 bps. The modem sends data to the telephone line
at 28.800 bps, this modem's maximum line speed.
Data is received by the remote
computer's 28.800 bps modem at 28.800 bps, and probably forwarded to the
Internet server at an unknown higher speed.
Why these differences in speed?
MNP level 5 compresses data
in the modem before transfer, and gives error- free transfer to and from
the Internet server at higher speed than by using 28.800 bps all the way
through.
The compression effectiveness
differs by the type of data. When sending text, the effective transfer speed
may double. Speed will increase further if the text contains long sequences
of similar characters.
Text is typically compressed
by up to 63 percent. This means that a 2400 bps modem using MNP-5 may get
an effective speed of around the double when transferring such data.
File transfers using MNP and V.42bis
Files are often compressed and stored in libraries before transfer. Online
services do this because compressed files take less space on their hard disks.
Also, it is easier for users to keep track of files sent in a library file.
You rarely get speed advantages
when transferring precompressed files using MNP or V.42bis. With some modems,
you must turn MNP and V.42bis compression off before retrieval of compressed
files.
Dumb or intelligent modem?
Some modems are operated with switches or buttons on a panel. They do not
react to commands from your computer. We call them dumb.
You must dial numbers manually,
and press a key on the modem, when you hear the tone from a remote modem.
Only when the modem is connected to the remote modem, can you ask your
communications program to take over.
We call those modems 'intelligent'
that can react to commands from your computer. Most of them react to commands
according to the Hayes standard.
Buy intelligent, Hayes-compatible
modems - even when other standards may seem better. Most of today's communication
programs are designed to be used by such modems.
Note: Buy modems that use the Hayes extended command set.
When a communications program, like Windows built-in Terminal, tells the
modem to "dial a number" or "go on hook," then the Hayes-compatible modem
will do just that.
When you click on Dialer and
Login in the Trumpet Winsock program, it will dial your Internet access provider
automatically. When you click on Dialer and Bye, it will ask the modem will
disconnect from the remote modem.
If you press ALT-D in the
communications program Telix followed by the number "2," then it will locate
the number to an online service in your telephone directory, and dial that
number.
When the connection with the
remote modem has been set up, your modem will report back to you with a message
like CONNECT 14400. This tells that a connection has been set up at 14400
bps.
If I select "k" from a menu
provided by my communications program's command scripts, then my system will
retrieve today's business news from Tokyo and put them up on my screen.
In the process, my system
tells the modem to do several things, including "call a number," "speed 28800
bps," "redial if busy," "go on-hook when done." The only thing that I have
to do, is press "k". The communications program and the modem will do the
rest.
Automatic communication is
impossible without an intelligent modem.
The Hayes standard
The U.S. company Hayes Microcomputer Products, Inc. pioneered command- driven
modems. Their Smartmodem became a success, and "Hayes compatibility" a standard
for intelligent modems.
Today, it is as unimportant
to buy a Hayes modem to get access to Hayes commands, as to buy an IBM PC
to run PC software.
Automatic dialing (autodial)
was one of Smartmodem's important features. The modem could call a number
and prepare for data communication, once a connection had been set up. If
the line was busy, it could wait a while and then redial. The operator could
work with other things while waiting for the equipment to be ready for
communication.
The modem had automatic answer
(autoanswer), that is, when someone called in, the modem could take the phone
off hook and set up a connection with a remote modem. The modem enabled a
connected PC to act as an electronic answering machine.
Hayes-compatible modems can
report call progress to the local screen using short numeric codes or words
like CONNECT, CONNECT 1200, CONNECT 2400, NO CARRIER, NO DIALTONE, BUSY,
NO ANSWER, RING etc.
There can be small differences
between such modems. The message DIALTONE on one modem may be DIAL TONE on
another. Most of the main progress messages, however, are the same across
brands.
The old Smartmodem had switches
used to configure the modem. Most modern Hayes-compatible modems come without
switches and have more commands than their ancestor.
Today's Hayes-compatible modems
have a core of common commands, the "real" Hayes-commands, and several
unstandardized additional commands. Here is an example:
A standard on the move
On the Quattro SB2422 modem, 2400 bps speed without automatic speed detection
is set by the command "AT&I1". The equivalent command on Semafor's UniMod
4161 is "AT+C0".
Automatic detection of speed
is a feature that lets the modem discover the speed of the remote modem to
set its own speed at the same level. (Other modems may use different commands
to set this.)
When I want Windows Terminal
to call a bulletin board, it first sends a sequence of Hayes commands to
the Semafor modem. These commands are stored in Terminal's settings (Click
Settings, Modem Commands. Originate to update or change them.)
The purpose of these commands
is to "configure" the modem before calling. It sends the following:
AT S0=0 +C0 S7=40 S9=4 &D2
The cryptic codes have the following meaning:
AT "Attention modem. Commands following.."
S0=0 No automatic answer
+C0 No automatic speed detection (fixed speed)
S7=40 Wait 40 seconds for an answer tone from
the remote modem.
S9=4 Wait 4/10 seconds for detection of carrier
&D2 Go on-hook if the DTR signal is being
changed.
If this command is sent to the Quattro modem, it will reply with "ERROR."
The code "+C0" must be replaced with an "&I1". The rest of the commands
are the same. (Note: when a modem responds with "ERROR," it has usually rejected
all commands sent to it!)
This setup is held in the
modem's memory when Terminal sends its dialing command: ATDT4737031378. AT
stands for ATtention, as above. DT stands for Dial Tone. Here, it is used
to dial the number 4737031378 using tone signaling (rather than pulse dialing).
The modem cable
If you have an external modem, you must connect your computer to the modem
with a cable. Some modems are sold without a cable.
This cable may be called a
serial cable, a modem cable, a RS232C cable, or something else. Make sure
that you buy the correct cable for your system.
Make sure that the connectors
at each end of the cable are correct. If a male connector (with pins) is
required in one end and a female (with holes) in the other, do not buy a
cable with two male connectors.
Some connectors have 9 pins/holes,
while others have 25 or 8-pin round plugs (Apple computers). Use a shielded
cable to make sure there is minimal interference with radio and television
reception.
At this point, some discover
that there is no place on the PC to attach the cable. Look for a serial port
at the rear of your machine, labeled MODEM, COMMUNICATIONS, SERIAL, or with
a phone symbol.
If you find no suitable connector,
you may have to install an asynchronous communication port in the box.
Connecting your equipment to earth
Secure your computer and modem against thunderstorms and other electrical
problems. Securing the electric outlet in the wall is not enough. Problems
can also enter through the telephone line.
Thunderstorms have sent electrical
pulses through the telephone line destroying four modems, three PC-fax cards,
one mother board, and at least one asynchronous communication port.
To prevent this from happening
to you, disconnect electrical and telephone cables from your equipment during
thunderstorms.
The communications program
A powerful communications program is half the job. In my case it's the whole
job. Most of my work is done automatically.
The communications program
will help you with the mechanical transportation of data in both directions.
It lets you store incoming information for later use and reduces the risks
of errors.
There are several basically
different types of communications programs:
-
Programs that connect you to an Internet access provider using the TCP/IP
protocol. Example: Trumpet Winsock. In some cases, this is all they do. Sending
email, looking up the World Wide Web, and transferring files are done using
various client programs, like Netscape or Mosaic. Other programs, like SlipKnot,
can connect and perform client functions.
-
General purpose asynchronous communications programs, like Windows Terminal.
These let you call a large range of BBSes, commercial online services, and
Internet hosts. Your dialog with the host can be manual, or governed by automatic
scripts. Connecting to the Internet using TCP/IP is rarely included.
-
Special purpose communications programs. These are canned programs designed
to do specific tasks on defined services. They are rarely useful on other
services, and for other applications.
Some items to consider when shopping general purpose programs:
-
Seriously consider buying automatic programs ('robots') for access to individual
online services, even if that means having to use several programs for different
applications. (Read Chapter 16 for more.)
-
Menus and help texts are important for novices, and in environments with
"less motivated personnel." Advanced users may find it boring.
-
Ability to transfer data without errors. The program should have transfer
protocols like XMODEM, Kermit, XMODEM/CRC, YMODEM and ZMODEM. The XMODEM
protocol is the most commonly used. You need these protocols if you want
to transfer compiled computer programs (for example, .COM and .EXE files).
They are also used when transferring compressed files, graphics and music
files. ZMODEM is considered the best protocol by many.
-
Does it let you tailor it to your taste/needs? Some programs let you attach
batches of commands to function keys and keystroke combinations. For example,
by having your computer call your favorite online service by pressing the
F1 key.
-
Does it let you "scroll back" information having disappeared out of your
screen? This may be useful when you want to respond while online to an electronic
mail message. The sender's address and name, which you need to respond, have
scrolled off the screen. If you cannot review the "lost" information, you
may have to disconnect and call back later to send your mail.
Connecting to the online service
The first couple of times, most people think that it is very difficult. Soon
it becomes a simple routine.
On some computers, you just
press a key, and that's it. On others, you have to call and press, and watch,
while things are happening. Cheap is often a synonym for more work.
If you have a dumb modem connected
to your personal computer, these are the typical steps that you must take:
-
Start your communications program and set it up, for example, with 28.800
bps, 8 bits word length, 1 stop bit, no parity. (This is a common setup.)
Then set the program to "online."
-
Call the desired number.
-
When you hear the tone from the remote modem in the phone, press DATA to
get the modems to connect to each other (that is, to start to "handshake").
-
A front panel indicator may tell you when the connection has been set up.
You can start transferring data.
With an MS-DOS computer, an automatic modem and a powerful program preset
for the job, the steps may be as follows:
-
Start the program and display the telephone directory. Select a service from
the list by pressing a number.
-
The modem will call automatically to the service. When the connection has
been set up, your user identification and password are sent at the prompts
for such information. When this is done, you are free to take control.
With an MS-DOS computer, TAPCIS, and an intelligent modem, you start by selecting
forums and services to access on CompuServe. Enter
'o' to upload and download programs, or 'n' to have it fetch new message
headers and messages. TAPCIS will dial the number, do the job, and tell you
when it's done. Meanwhile, you can go out to look at the moon, or sing a
song.
Getting started with Procomm
Procomm is cheap and a popular communications program for MS-DOS computers.
We will use the old shareware version as an example here, though there are
many better and cheaper alternatives.
The program is simple for
novices, can automate the work for advanced users and be run on almost any
MS-DOS computer. Here are some of its features:
Press ALT-F10 for a pull-down
window text listing features and commands. Press ALT+D to call a number,
update the telephone directory, or select a script file for autologon to
a service.
Procomm can emulate (pretend
to be) different terminal types, like IBM 3101 and DEC VT-100/VT-52. Most
services covered in this book may be well served with the setting ANSI.BBS.
It let you use both dumb and
intelligent Hayes-compatible modems. If you have the latter, select numbers
from the telephone directory for autologon. If the number is busy, Procomm
can call back until you can get through.
You can define macros to automate
your work. You can have one keystroke send your user identification, another
for your password, and a third key to send a sequence of commands. Macros
make your communication faster and safer.
You can write script files
to automate the online work further. You can transfer text files and binary
files using automatic error detection/correction protocols, like XMODEM,
YMODEM, Telink and Kermit, at speeds from 300 to 19200 bps. Adding external
protocols like ZMODEM is relatively simple. |
