Possibilities - Taking the Buzz Out of Buzz Words - Part 1

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TAKING THE BUZZ OUT OF BUZZ WORDS - PART 1
------------------------------------------

*** From July 1990 Possibilities Newsletter ***
*** Copyright 1990 by eSoft, Inc.  All Rights Reserved ***

Taking The "Buzz" Out of Buzz Words
Part 1: The Basics of Modems
by Alan D. Bryant

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 Bryant 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!

- END -
PS0790-7
Rev. 7/90

Copyright (C) 1994 eSoft, Inc., All Rights Reserved.  Permission granted
to distribute this file in its entirety, without modification, to any
interested party.  Any other use requires the written permission of
eSoft, Inc.

IMPORTANT:  The information herein is subject to change without notice.
Please call or write to confirm factual information of importance to you
or your organization.

