Taking The "Buzz" Out of Buzz Words
by Alan D. Applegate
Copyright 1990 by eSoft, Incorporated.
All Rights Reserved
---------------------------------------------------------------
Note:  The following three part series on modem fundamentals is 
reprinted with permission from the eSoft possibilities newsletter 
June, July, and August 1990 issues.  Possibilities is a monthly 
customer support publication of:

   eSoft, Incorporated
   15200 E. Girard Avenue
   Suite 2550
   Aurora, Co 80014

This series of articles may not be reproduced in any form except 
by inclusion of the above copyright notice.  This file is 
authorized for distribution without charge only if it is 
unchanged in any way.  Any use of this information in any other 
way must include proper credit to its source.
---------------------------------------------------------------

                  Part 1: The Basics of Modems
                  ----------------------------

[The world of computers is riddled with buzz words -- technical 
jargon for the various parts of computers, their functions, and 
applications.  In telecommunications it's the same thing.  Terms 
like Baud, Bits, Parity, MNP, Half Duplex, and Full Duplex can 
make a TBBS system designer's life seem more complex than it 
really is.  The problem is, these buzz words are attached to many 
of the components and concepts that a TBBS system designer must 
grasp to make the most of online system implementation and even 
to explain a system's operation to its users.

Fortunately, most telecommunications terminology isn't hard to 
understand -- once it's been explained by someone who knows what 
the terms mean and can speak English clearly enough to break them 
down in understandable language.  Alan Applegate is just such a 
person and we at eSoft are lucky enough to have him on our 
technical support staff.

In the following special three-part series, Alan will tackle many 
of the common telecommunications buzz words you'll encounter as a 
TBBS system designer and bring them a lot closer to home with 
straightforward, plain-English definitions and step-by-step 
explanations... Ed.]

Modem Standards
---------------
No doubt you've wondered at one time or another about modem 
standards.  There are currently several active standards, and 
they involve more than just the modem's actual operating speed.  
Without these standards, modems from one manufacturer most likely 
couldn't "talk" to modems made by another manufacturer.  
Consequently, at least a basic understanding of modem standards 
is also necessary if you want to make the right choices when 
selecting modems for use on your TBBS system.

Generally speaking, 300, 1200 and 2400 bps modems each use a 
different standard that is adhered to by all modems and modem 
makers.  (It should be noted that standards for 300 and 1200 bps 
are different in the United States than they are in Europe.)

Standards for 9600 bps transmission have been established for 
some time, but the technology to implement those standards was, 
until recently, expensive.  To get around the high cost of using 
the existing standard, modem manufacturers have created several 
of their own proprietary high-speed modem standards.  This is why 
so many high-speed modems will only "talk" to another high-speed 
modem of the same brand.

Data transmission speeds, however, are not the only type of modem 
standard.  Actually, modem standards are grouped into four 
distinct areas or "layers."  These are shown in the illustration 
below:

Modulation
----------
Modulation is the starting (or bottom) layer for all modems  
("modem" means MOdulator - DEModulator). Each layer builds upon 
the next.

Modulation refers to the signaling method that is used by the 
modem.  Two modems must use the same modulation method in order 
to understand each other.  Each data rate uses a different 
modulation method, and sometimes there is more than one method 
for a particular rate.  An example of this is the Bell 212A and 
V.22 modulation standards (described below); they both specify 
1200 bps modulation, but they work differently, and are not 
directly compatible.

Negotiation
-----------
Negotiation refers to the manner in which two modems establish 
which modulation method will be used during a connection.  Modems 
"listen" to the tones sent by a remote modem to determine what 
modulation method will be used.  Since different modulation 
methods often use different answer tones, these can be used by 
the calling modem to determine which method to use.  Negotiation 
standards have been created to make the process easier.  These 
standards dictate the sequence of events that will occur when a 
modem answers the phone, eliminating the guesswork associated 
with the "listen to the tones" method.  Negotiation is part of 
many modem standards.

Error Correction
----------------
Error correction refers to an ability that some modems have to 
identify errors during a transmission, and to automatically re-
send data that appears to have been damaged in transit.  If error 
correction is used, both modems must adhere to the same error 
correction standard to make it work.  Fortunately, there are 
error correction standards which are followed by most modem 
manufacturers.

Data Compression
----------------
Data compression refers to a built-in ability in some modems to 
compress the data they're sending, automatically "squeezing" data 
to a smaller size as it is sent.  This, of course, saves time and 
can result in considerable money saved by long-distance modem 
users.  Depending on the type of files that are sent, data can be 
compressed by as much as 50% of its original size, effectively 
doubling the speed of the modem.

In this scenario, a 2400 bps modem with data compression is 
capable of sending some files as quickly as a 4800 bps modem 
WITHOUT data compression. Not all types of data can be compressed 
by 50%, but gains can nearly always be realized.

We'll take a look at each of the various data compression 
standards later in this series, but first let's examine those 
modem standards that are associated directly with the 
transmission speed of the modem.

Standards for 300 and 1200 Bps
------------------------------
Most 300 bps modems follow the standard created initially by 
AT&T, called Bell 103, and are common in the United States.  Most 
modems manufactured for use outside the United States support the 
CCITT V.21 standard instead, and are not compatible with Bell 103 
modems.  Some modems can be set to follow either standard.

AT&T also created the Bell 212A standard for 1200 bps modems.  
It's become the common standard in the United States.  Most 
modems manufactured for use outside the United States support the 
CCITT V.22 standard instead, and are not compatible with the Bell 
212A modems.  Some modems can be set to follow either standard.  
Most modems manufactured since 1985 are capable of 
differentiating between the two standards, and can effectively 
handle either one. 

2400 Bps Standards
------------------
The international standard for 2400 bps communications is CCITT 
V.22bis.  This is used by modems manufactured for use both inside 
and outside the United States.  Most 2400 bps modems include 
automatic detection of the data rate fall back, if a data rate 
lower than 2400 bps is detected at the other end of the 
connection.

9600 Bps Modems -- Are There Standards?
---------------------------------------
Contrary to what might be believed, standards for high speed data 
transmission have been in place for some time.  Acknowledged 
standards came in two forms -- a half duplex standard, commonly 
used in fax machines and called V.29, and a full duplex standard 
called V.32 (we'll take a look at half and full duplex later in 
the series).  The technology required to implement the V.32 
standard remained prohibitively expensive for many years.  This 
forced most modem manufacturers to create their own less-
expensive proprietary transmission methods.

U.S. Robotics, for example, created the Courier HST, ("High Speed 
Technology").  This design is not full duplex, meaning that it 
does not support high speed transmission in BOTH directions.  
Current HST modems send data at 14,400 bps in one direction, and 
450 bps in the other direction.  The high speed channel changes 
direction depending on which side of the transmission has the 
most data to send.  HST modems can only talk at high speed with 
other HST modems, although they also adhere to existing standards 
for 300, 1200 and 2400 bps operation.

Telebit, another modem manufacturer, created PEP ("Packetized 
Ensemble Protocol"), which is used in their Trailblazer modem 
series.  Like the HST, PEP modems will only connect at high speed 
with other PEP modems.

Hayes also developed their own technology for high speed 
transmission, in the absence of an inexpensive standard.  Like 
the others, Hayes high speed modems only talk high speed to other 
Hayes modems. 

Fortunately, the cost of V.32 high speed transmission technology 
has come down drastically in recent years, and is displacing 
other high speed proprietary protocols in popularity.  This means 
that, finally, high speed modems are starting to communicate with 
a common standard.  U.S. Robotics' new Courier HST Dual Standard 
is one example of a new high speed modem utilizing both U.S. 
Robotics' own HST transmission standard and the V.32 high speed 
standard.  The new Hayes V-series Ultra Smartmodem 9600 is 
another "multiple-standard" high speed modem that utilizes the 
V.32 standard.

Next month we'll discuss the CCITT and the international 
telecommunications standards that are set by this prestigious 
committee.  We'll even de-mystify the whole family of MNP 
standards.  Also we'll examine the data compression standards.  
What works, what doesn't and what is realistic to expect from 
data compression in a modem?  MNP vs. V.42bis -- don't 
miss it!


                     Part 2: Modem Standards
                     -----------------------

The CCITT is the acronym for the Consultative Committee on 
International Telephone and Telegraph.  This is an international 
body of technical experts responsible for developing data 
communications standards for the world.  The group falls under 
the organizational umbrella of the United Nations and its members 
include representatives from major modem manufacturers, common 
carriers (such as AT&T), and governmental bodies.

CCITT Modulation Standards
--------------------------
The CCITT establishes standards for modulation -- actual modem 
signaling methods.  It also determines standards for error 
correction and data compression (See part 1 of this series for a 
full description of these modem layers).  For this reason, it is 
possible (and likely) that one modem might adhere to several 
CCITT standards, depending on the various features and 
capabilities the modem offers.

All modems signal one another at a variety of speeds, so CCITT 
standards for modulation are utilized by virtually every modem 
manufacturer.  Some of the standards which are primarily 
modulation do include some of the higher layers (such as 
negotiation) as well.  Multi-speed modems may use several of 
these standards, which include:

V.21
----
V.21 is a data transmission standard at 300 bps.  This standard 
is used primarily outside of the United States.  (300 bps 
transmissions in the United States primarily use the BELL 103 
standard).

V.22
----
V.22 is a data transmission standard at 1200 bps.  This standard 
is also used primarily outside of the United States.  (1200 bps 
transmissions in the United States primarily use the BELL 212A 
standard).

V.22bis
-------
V.22bis is a data transmission standard at 2400 bps.  This is the 
international standard for 2400 bps, and is used both inside and 
outside the United States.

V.23
----
V.23 is a split data transmission standard, operating at 1200 bps 
in one direction and 75 bps in the reverse direction.  Therefore, 
the modem is only "pseudo- full-duplex," meaning that it is 
capable of transmitting data in both directions simultaneously, 
but not at the maximum data rate.  This standard was developed to 
lower the cost of 1200 bps modem technology, which was still very 
costly in the early 1980s, when such modems were designed.  This 
standard is still in use, but primarily in Europe.

V.29
----
V.29 is a data transmission standard at 9600 bps which defines a 
half duplex (one-way) modulation technique.  Although modems do 
exist which implement this standard, it has generally only seen 
extensive use in Group III facsimile (FAX) transmissions.  Since 
it is a half-duplex method, it is substantially easier to 
implement this high speed standard than it would be to implement 
a high speed full-duplex standard.  V.29 is not a complete 
standard for modems, so V.29-capable modems from different 
manufacturers will not necessarily communicate with one another.  

V.32
----
V.32 is also a data transmission standard at 9600 bps, but V.32 
defines a full-duplex (two-way) modulation technique.  It is a 
full modem standard, and also includes forward error correcting 
and negotiation standards as well.  Many modem manufacturers 
already have or will be introducing V.32-compatible modems.  This 
is generally considered "the" standard for high-speed modems 
today.

V.32 is expensive to implement, since the technology required for 
it is complex.  As this standard becomes more common and 
manufacturing techniques are refined, the pricing for V.32 modems 
should go steadily downward.  At this writing, V.32 capable 
modems are selling for between $500 and $1000 each.

Some manufacturers have created modems that can use both their 
own proprietary high speed standard and the V.32 standard, for 
compatibility with their older non-V.32 modems.  The new Hayes 
Ultra and U. S. Robotics HST Dual Standard are examples of the 
new "dual personality" modems that are now on the market.

V.32bis
-------
This is a developing high speed standard.  When fully defined 
(likely by early 1991), V.32bis will operate at 14,400 bps and, 
like V.32, will be a full-duplex method.  The CCITT has not yet 
defined this standard, so no modems currently use it (although 
some new modems have implemented what is expected to be the 
standard and may claim V.32bis compatibility).

Error Correcting and Data Compression
-------------------------------------
The CCITT also has adopted formal standards for the higher layers 
of Error Correction and Data compression (See Part 1 of this 
series for a full description of these layers).  In order for any 
error correction or data compression protocol to work, modems on 
BOTH ends of the connection must support it.  Once two modems are 
connected, they automatically negotiate between themselves to 
determine the best mutual protocols they both support.

V.42
----
V.42 is a CCITT error-correction standard that's similar to MNP 
Class 4 (See "What is MNP" below).  In fact, because the V.42 
standard includes MNP compatibility through Class 4, all MNP 4-
compatible modems can establish error-controlled connections with 
V.42 modems.  This standard, however, prefers to use its own 
better performing protocol -- LAPM (Link Access Procedure for 
Modems).  LAPM, like MNP, copes with phone line impairments by 
automatically re-transmitting data that is corrupted during 
transmission assuring that only error free data passes through 
the modems.  Many modem manufacturers make MNP Class 4-compatible 
modems, and some offer V.42-compatible modems as well.

V.42bis
-------
V.42bis is a CCITT data compression standard similar to MNP Class 
5, but providing about 35% better compression.  Of course, this 
also means it provides better throughput.  V.42bis only 
compresses data that needs compression.  Each block of data is 
analyzed, and if it can benefit from compression, compression is 
enabled.  Files on bulletin board systems are often compressed 
already (using ARC, PKZIP, and similar programs).  While MNP 
Class 5 can actually decrease throughput on this type of data, 
V.42bis will not -- compression is only added when a benefit 
will be realized.

To negotiate a standard connection using V.42bis, V.42 must also 
be present. Thus, a modem with V.42bis data compression is 
assumed to include V.42 error correction.  Some modem 
manufacturers already make V.42bis compatible modems, and more 
are on the way.

V.42bis is NOT compatible with MNP Class 5.  A V.42bis modem will 
establish an error-free connection with MNP-capable modems (since 
V.42bis includes V.42), but only up to MNP Class 4.  

What is MNP?
------------
MNP stands for "Microcom Networking Protocol" and was created by 
Microcom, Inc., a modem manufacturer.  MNP offers end-to-end 
error correction, meaning that the modems are capable of 
detecting transmission errors and requesting re-transmission of 
corrupted data.  Some levels of MNP also provide data 
compression.

As MNP evolved over time, different classes of the standard were 
defined, describing the extent that a given MNP implementation 
supports the protocol.  Most current implementations support 
Classes 1 through 5.  There are higher classes, but are usually 
unique to modems manufactured by Microcom, Inc. since they are 
still proprietary.

MNP is generally used for its error correction capabilities, but 
MNP Classes 4 and 5 also provide performance increases, with 
Class 5 offering real-time data compression.  The lower classes 
of MNP are not usually important to you as a modem user, but they 
are included here for completeness.

MNP Class 1
-----------
MNP Class 1 is referred to as Block Mode.  It uses asynchronous, 
byte- oriented, half-duplex (one way) transmission.  This method 
provides only about 70% efficiency.  It provides error correction 
only, and is rarely used today.

MNP Class 2
-----------
MNP Class 2 is called Stream Mode, and uses asynchronous, byte-
oriented, full- duplex (two way) transmission.  This class also 
provides error correction only.  Because of protocol overhead 
(the time it takes to establish the protocol and operate it), 
throughput at Class 2 is actually only about 84% of that for a 
connection without MNP, delivering about 202 cps (characters per 
second) at 2400 bps (240 cps is the theoretical maximum).  Class 
2 is rarely used today.

MNP Class 3
-----------
MNP Class 3 incorporates Class 2, and is more efficient.  It uses 
a synchronous, bit-oriented, full-duplex method.  The improved 
procedure yields throughput about 108% of that of a modem without 
MNP, delivering about 254 cps at 2400 bps.

MNP Class 4
-----------
MNP Class 4 is a performance enhancement class that uses Adaptive 
Packet Assembly(tm) and Optimized Data Phase(tm) techniques.  
Class 4 improves throughput and performance by about 5%, although 
actual increases depend on the type of call (local or long-
distance, noisy or clean connection), and can be as high as 25% 
to 50% on some links.

MNP Class 5
-----------
MNP Class 5 is a Data Compression protocol which  uses a real-
time adaptive algorithm.  It can give an increase of up to 50% in 
throughput, but the actual performance of Class 5 is very 
dependent on the type of data being sent.  Raw text files will 
allow the highest increase, while program files cannot be 
compressed as much and the increase will be less.  On pre-
compressed data (files already compressed with ARC, PKZIP, etc.), 
MNP 5 can actually EXPAND the data and performance can actually 
decrease.  For this reason, MNP 5 is often disabled on BBS 
systems.

MNP Class 7
-----------
MNP Class 7 is the other major MNP protocol you are likely to 
encounter.  MNP 7 provides Enhanced Data Compression.  When 
combined with Class 4, it can obtain about a 300% improvement in 
performance.  It is designed primarily for use with V.22bis (2400 
bps) modem.  This class is currently unique to Microcom modems.  
Since it requires much more hardware and is usually inferior to 
V.42bis, it is not likely to proliferate.

What does it all mean?
----------------------
Despite the fact that they can seem quite confusing, all of these 
standards exist to benefit you the modem user.  You want to be 
able to compare modems on price, reliability, performance, and 
support.  You also want to be able to know that modems from 
different manufacturers will communicate with each other.

The past couple of years in the high speed modem arena has shown 
what happens when market demand occurs faster than associated 
standards.  You are forced to pick a single manufacturer and 
become locked in to gain the capabilities you want.  The purpose 
of standards is to prevent this situation.

When standards are widely adopted, you get the best of technology 
and competition.  However, you need to know what the standards 
mean to be able to be an informed consumer.

Next month we'll wrap up this discussion with explanations of 
most of the rest of the various terminology common to the modem 
world, but not always fully understood.  Don't miss it!


                Part 3: Communication Terminology
                ---------------------------------

Of Bits and Parity...
---------------------
In parts 1 and 2, we took a closer look at the most common and 
often least understood terms and standards in the world of the 
modems we use.  There are, however, several other 
telecommunications terms that can be confusing.  Though they 
don't necessarily relate to modem-buying decisions specifically, 
understanding these terms can add important additional power to 
your communications dealings.  They also will help you understand 
how to set up the terminal programs your users will have to 
configure to call your TBBS system.  Among the most commonly 
faced (and least understood) are the concepts of Data Bits, 
Parity, and Stop Bits.

Data Bits
---------
The American Standard Code for Information Interchange - ASCII - 
is a standard that defines 128 different characters that can be 
used for data transmission.  These include control characters, 
letters of the alphabet (in both upper and lower case), numbers, 
and a full set of punctuation characters.  Because there are only 
128 ASCII characters, only 7 binary digits (bits) are required to 
form each of the 128 possibilities.

Many computer makers have extended the ASCII character set by 
adding 128 more characters.  This was accomplished by simply 
adding one more binary digit,  resulting in a total of 256 
transmittable data characters.  Each manufacturer, however, 
created their own set of 128 additional characters.  All extended 
character sets are NOT the same.

In the case of the IBM PC and compatibles, the extended 
characters include international alphabet, graphics and 
mathematics characters.  These are commonly known as IBM Graphics 
characters.

In communications, common settings are either for 7-bit or 8-bit 
data.  Generally, both ends of the connection must be set the 
same way.  If one end is set to 7-bit data and the other end is 
set to 8-bit data, reliable communication cannot usually be 
established.  This is because one end interprets the 8th data bit 
as a parity bit (explained in a moment), and the other end tries 
to interpret it as a part of the current character.  On a 
connection like this, some characters will display properly, 
while others will appear as "garbage," depending on which 
direction the data is traveling.

If the communications link is set to transmit only 7-bit data, 
the sendable characters are limited to the 128 defined ASCII 
characters.  The extended character set, such as the PC's single- 
and double-line boxes and foreign characters, CANNOT be sent 
unless the link is first set to allow the transmission of 8-bit 
data.

Some systems have even 5-bit and 6-bit data, and use character 
sets such as Baudot and Selectric, but these systems are uncommon 
today.

Parity Bit
----------
When you establish communications with another computer, parity 
is set to "even," "odd," "mark," "space" or "none."  These are 
terms for the manner in which the parity bit is interpreted by 
the receiver.

Parity is a primitive form of error-checking.  The state of the 
parity bit, when set to be even or odd, is based on a simple 
mathematical formula.  Depending on the data bits, the parity bit 
will either be on or off.  Normally, the limited error checking 
capabilities are not utilized.  This explains why the setting of 
parity to "none" is so common in communications today.  This 
allows the parity bit to be used as a normal data bit instead.

Start and Stop Bits
-------------------
Start and stop bits allow each character sent to be set in a 
"frame."  The beginning of the character, the first part sent, is 
the start bit, and the end of the character, the last part sent, 
is the stop bit.  Each character sent is thus framed with a 
distinct beginning and ending bit and this allows the receiving 
system to know when each complete character has been sent.

There is always just one start bit.  However, there may be one, 
one and a half or two stop bits.

Stop bit length used to be critical when serial communication was 
primarily handled with electromechanical equipment, such as an 
old-fashioned Teletype machine.  The print head in this type of 
equipment took a fixed amount of time to return to its "home" 
position, and this was accomplished during the sending of the 
stop bits.  A longer stop bit length gave the print head more 
time to return to its home position.

In modern all-electronic serial communication, the stop bit is 
still necessary, but only to mark the end of a character.  A 
delay isn't necessary as there isn't usually anything mechanical 
involved.

Asynchronous Communications
---------------------------
Framing the character with start and stop bits forms the basis 
for "asynchronous" communications.  In asynchronous transmission, 
characters do not have to flow constantly - there can be "gaps," 
or spaces, between each character.  The receiver knows when a 
character is sent by the framed nature of asynchronous 
transmission - the start and stop points can easily be 
determined.

Synchronous Communications
--------------------------
An alternate serial transmission method exists known as 
synchronous communications.  It occurs when there are no start or 
stop bits, and is possible only if data characters flow 
constantly at a fixed bit rate with no interruptions.  When there 
is no data to send, idle or padding characters are sent at the 
fixed rate (to keep data bits flowing constantly), but they are 
discarded by the receiver.

Because there are no start or stop bits, it is possible to remove 
2 of every 10 bits used in Asynchronous communications.  This 
results in a 20% faster data speed with the same serial bit rate.  
However, because of the requirement for constant data flow, 
Synchronous transmission requires additional protocol and is 
primarily used in mainframe computer or specialized applications.

One place it is used with TBBS is hidden inside of high speed 
modems.  When these modems use MNP or V.42 protocols, they have 
the needed protocol to use synchronous communications between the 
modems themselves.  However, you still use asynchronous 
communications between the computer and the modem so this 
instance of hidden synchronous communications is primarily of 
interest as trivia.

Duplex
------
"Duplex" is a term which refers to whether a data communications 
path is one- way or two-way.  "Full duplex" means that data can 
flow in both directions at the same time.  "Half duplex" means 
that data can flow in only one direction at one time.  Most 
modems are full duplex, but communications software can most 
often still be set to take advantage of half duplex connections.

Some less expensive high speed (9600+ bps) modems are pseudo- 
full-duplex.  This means they cannot transmit data at high speed 
in both directions at the same time because they are really 
operating in a fast turn-around half duplex mode internally.

Flow Control
------------
The term "flow control" refers to a method of controlling the 
flow of transmitted data, so it doesn't "overrun" the data 
receiver's ability to receive the incoming signals.  Flow control 
allows the receiver to signal the transmitter to pause, while 
recently received data is properly assimilated, then signal it to 
restart the data flow when it's ready to receive more.

There are generally two forms of flow control - software and 
hardware.

RTS/CTS
-------
Hardware flow control is not always required.  It is generally 
needed only with modems that are capable of "buffering" out-going 
data, or with high speed modems.  Hardware flow control, called 
RTS/CTS flow control, uses two of the RS-232 (serial) pins to 
start and stop the data flow.  Its advantage is that it is data 
independent and thus can be used for reliable flow control with 
any type of data stream.

X-ON/X-OFF
----------
Software flow control, called XON/XOFF flow control, starts and 
stops the data flow based on the reception of certain control 
characters.  Although this type of flow control can be used by 
hardware devices, software flow control is usually used with 
TBBS, to allow the TBBS user to start and stop data transmission 
by using control keys.  This allows the user to press Ctrl-S at 
any time to temporarily halt data flow, and then press Ctrl-Q at 
any time to restart data flow.  

Even when hardware flow control is in use, TBBS will honor 
software flow control codes to start and stop the flow of text 
data displays.

What is ANSI?
-------------
"ANSI" is a common term in the bulletin board community today, 
but it's also a term that's usually misused.

ANSI stands for the American National Standards Institute, a 
standards development organization (sort of like the CCITT, which 
I discussed in my last column).  ANSI develops and documents 
standards for thousands of different areas, from architectural 
specifications for the handicapped to computer programming 
languages.

Within the bulletin board community, the term "ANSI" generally 
refers to an ANSI standard called X3.64 as implemented by IBM in 
ANSI.SYS.  The ANSI X3.64 standard specifies a series of codes 
that a host system can send to a remote data terminal to control 
color attributes, cursor positioning, inverse video and screen 
clearing on the terminal display.  

"ANSI Graphics" is a term that is often used in the bulletin 
board community, but this actually refers to two separate 
elements.  "ANSI" controls color and cursor positioning, while 
"Graphics" usually refers to characters in the IBM PC extended 
character set, such single- and double-line boxes, shading 
characters, and so on.  "ANSI Graphics" is a common term, since 
normally only an IBM PC is capable of handling both ANSI and 
Graphics.  In reality, many data terminals and software packages 
for various computers are capable of handling ANSI codes, 
although they may not always handle the IBM extended characters.

Actually, "ANSI Graphics" does NOT refer to a standard for 
displaying pictures or graphic images on the remote terminal.

The VT-100 terminal (a data terminal from Digital Electronics 
Corporation) and software that emulates a VT-100 terminal can 
also be used with ANSI escape codes, since the codes for both 
ANSI and VT-100 are very similar.

ANSI works by sending a series of characters to the remote 
terminal.  The codes all begin with an escape character and a 
left bracket, and are followed by a variable quantity of numbers 
and letters.  The terminal understands the meaning of these 
codes, and acts accordingly by setting screen colors or moving 
the cursor.

Graphics
--------
Graphics, as I mentioned previously, are the characters in the 
IBM PC extended character set.  They are characters beyond the 
original 127 possible ASCII characters as defined by IBM in all 
of their display adapters.  These include single- and double-line 
boxes, shading characters, international characters and 
mathematical symbols.

IBM Graphics characters have become enough of a de-facto 
standard, that many other computers now emulate them.  Many 
terminal programs on the Apple Macintosh computer will allow 
proper display of the IBM graphics character set, as will many of 
the true display terminals on the market today.

Summary
-------
That pretty well covers most of the common modem and 
telecommunications program terms and standards in use today.  I 
hope this series of articles has made you better able to 
understand the seemingly endless number of buzz words you find in 
microcomputer communications. You should now be able to 
understand better why terminal programs must be configured to 
operate correctly.  You also should be able (with information 
from the first two parts of this series) to better choose the 
type of modem you need to meet your applications.  I hope you'll 
let us know if you have any questions or need further help 
understanding anything that I've already discussed.  It's been 
fun...
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