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                                    8
                                



                                  Modem 
 






















Help Guide to Buying a Computer





Chapter 8 - Modem


     A modem (short for MODulation/dEModulation) translates "computer
language" to and from something your normal telephone will understand so you can
use the telephone line to talk to another computer.  Modems have grown in
popularity during the last decade due to a number of reasons such as lower
prices, higher speeds, smaller sizes and the number of people and businesses 
using on-line services (like the Internet, CompuServe or America On-Line).   If 
you want to call the office with your computer or connect to any on-line 
services, then you must have a modem

     Modems are classified by how fast (how much) they can send or receive data
in a second and this is called the modem's kbps (KiloBits Per Second).  For
example: a 28.8kbps (also written 28,800bps) modem transfers (sends or receives)
28,800 bits per second.  28.8kbps is currently the fastest standard two-way 
modem speed available, and it is what you would want in a modem.
     
     If you're going to buy a modem then your best bet is to buy a V.34
(28.8kbps) modem and not a V.FC (28.8kbps) modem.  Why?  Simply because a
V.FC modem may not be able to connect to everyone you want to call.  Now I don't
mean a V.34 modem that also supports V.FC.  That's fine.  You simply don't want 
a modem that only supports V.FC and not V.34.  If you want more detail on why
V.FC is bad then read the following paragraph.  

     In 1993 a new modem standard called V.FC (Fast Class) emerged and was at
that the time the fastest standard available, but it was and still is a complete 
disaster.  V.FC was the early version of what is now called V.34.  While the 
V.34 standard was evolving, and long before it ever became a "true world-wide" 
accepted standard, many modem manufacturers jumped the gun and introduced their 
own version of V.FC.  Here's the kicker; since each modem manufacturer used 
their own version (and set of rules) to develop their V.FC modem, most of the 
V.FC modems wouldn't properly work with other V.FC modems from other 
manufacturers.  The whole reason for standards is so the modem from one 
manufacturer can talk to the modem from another manufacturer.  V.FC is called a 
standard, but it never really was, since very few modem manufacturers agreed on 
the specifics of the V.FC standard.
















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Chapter 8 - Modem


     In the summer of 1994, the V.34 standard was finally complete and accepted
by the world as a true standard.  Since that time, most of the modem 
manufacturers that developed V.FC modems have gone back and updated them so they 
work correctly with the V.34 standard.  Most V.FC modem manufacturers have or 
are still offering some type of upgrade so users that own V.FC modems can get 
V.34 modems.  

     If you're in the market for a modem, don't buy a V.FC modem because as I
explained above; you'll have problems!  Consider some of the following reasons
why V.34 is superior to V.FC:

    -     V.34 modems are cheap these days so the few bucks that you would save 
          by buying anything less wouldn't be worth the trouble you're likely to 
          encounter with other modems that won't work with V.FC modems.
    -     V.34 performs better (can send or receive at a faster pace) on noisy 
          phone lines (modems like quiet phone lines).
    -     V.34 can adjust faster to adverse phone line conditions (your daughter 
          picks up the phone while your modem is dialed into the office 
          computer).
    -     You can count on other V.34 modems being compatible with your V.34    
          modem.

     Each modem speed (like 28.8kbps) requires some type of communications
standard behind it (like V.34) so each modem knows what "language" it is 
supposed to speak and understand.  These types of standards have been around 
since the very first modems were invented.  Figure 8a shows most of the more 
recent standards, and what speeds (how fast the modem can send and receive) are 
possible when using these standards to talk to another modem.

     New computers are likely to have some type of modem included, but beware
because not all modems are equal (see Figure 8a).  Several years ago modem
manufacturers started building fax computer cards and modem cards into one card. 
The result was the ability to also send and receive faxes with your computer in
addition to the modems capability.  It was a great idea and I'm very happy most
modem manufacturers still do this today.  Unfortunately, several computer
manufacturers will offer with their computers a 2400/9600 fax/modem and that














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Chapter 8 - Modem


means the modem runs at a maximum of 2400bps while the fax portion run at a
maximum of 9600bps.  Don't be impressed because that modem is only worth five
bucks.  By today's standards, that fax/modem stinks!  The average fax/modem 
today runs at 14.4kbps/14.4kbps (also written as 14.4/14.4) and the better cards 
are 28.8kbps/14.4kbps.  14.4kbps is currently the highest fax speed.  Comparing 
the times required to transfer one document file on a 2400bps modem verse the 
same document on a 28.8kbps modem shows the 28.8kbps modem can transfer (or
receive) that document in 1/12 the time.  Yes, really!  Just imagine the 
difference in your waiting and long distance charges!  The difference in price 
between average fax/modems (14.4/14.4) and the better 28.8/14.4 fax/modems isn't 
more than about $50 so if you're in the market for a modem, do yourself a big 
favor and get the 28.8kbps version.  You'll be happy you did.

     Modems often have what's called a theoretical throughput number.  Don't get
fooled by this.  This number is simply the absolute largest possible, under 
perfect conditions (Are your phone lines perfect?  I think not!) number of kbps 
the modem can send or receive. The number is almost always four times the rated 
kbps of the modem.  In other words:

     *    A 2400bps modem has a theoretical send and receive ability of 9600bps.
     *    A 14.4kbps modem has a theoretical send and receive ability of 
          57.6kbps.
     *    A 28.8kbps modem has a theoretical send and receive ability of             
          115.2kbps.

     I've listed below the minimum features you should expect from your modem.   
Since a 14.4kbps modem is considered an average modem these days, and you really
should be buying a 28.8kbps modem (because of the speed and small price tag), 
I've only included features for these two modem speeds.  Somewhere on the 
fax/modem box you should see a list of the supported standards (the things 
listed below).  If you're buying the computer, and it has a fax/modem in it then
ask the computer dealer if the modem is compatible with the following list of 
standards.  If it isn't then you don't want it! 

















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Chapter 8 - Modem


                     Modem Speeds and Standards

          ------------------------------------------------------------
          |
  V.34bis |*************************************************** 33,600
          |
     V.34 |******************************************* 28,800
          |
V.32terbo |**************************** 19,200
          |
  V.32bis |********************* 14,400
          |
     V.32 |************* 9,600
          |
     V.42 |*** 2,400
          |
 Bell 103 |* 300
          |
          ------|-------|-------|-------|-------|-------|-------|-----
           0   5000   10000   15000   20000   25000   30000   35000


Figure 8a - The vertical axis shows the standards that allow the modems to
            operate at the speeds shown on the horizontal axis.  The speeds on
            the horizontal axis are all in bps and not kbps (ie. 28,800bps is
            the same as 28.8kbps).  V.32terbo is another standard that never
            caught on (ie. you don't want it!), but I included it to show the
            speed difference between it and V.34.
          





















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Chapter 8 - Modem


A list of the minimum features you should expect from a new fax/modem:

                    14.4kbps            28.8kbps
                    --------            --------

Modem section:      V.32bis             V.34
                    V.32                V.32bis
                    V.42bis             V.32
                    V.42                V.42bis
                    V.22bis             V.42
                    V.22                V.22bis   
                    MNP 2-5             V.22
                    16550 UART *        MNP 2-5
                                        16550 UART *

Fax section:        Class 1 & 2         Class 1 & 2
                    V. 17 (Group III)   V. 17 (Group III)
                    V.29                V.29
                    V.27ter             V.27ter
                    V.21                V.21


    Note: A UART is a special chip which allows the modem or fax to operate at
          certain speeds.  Currently, a 16550 UART is the best (fastest) and         
          what your 14.4kbps or 28.8kbps MUST have.  If it has a 16450 then          
          don't buy it regardless of what they tell you!


     Even before the V.34 standard had been approved, speculation had already
started on how modems could be made to go even faster.  As I (and a number of 
other people) predicted, this came about in the form of V.34bis.  V.34bis is 
based on V.34, but has been "tweaked" to deliver up to 33.6kbps (compared to 
28.8kbps with V.34) and has just recently become available on the market.  In 
fact, only a few modem manufacturers currently support it.  Since V.34bis is 
expected to become an accepted standard, I have included it in Figure 8a.

     Remember, the faster the modem then the faster you can send or receive 
files, messages, etc.  This is true only if your modem is talking to a modem 
just as fast as it is.  Consider Figure 8b.











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Chapter 8 - Modem


DATA
SPEED       COST      Total time required in minutes



28,800bps    $0.34    |* 1.4
                      
14,400bps    $0.72    |** 2.9
                      
 9,600bps    $4.32    |************* 17.3
                      
 2,400bps   $17.33    |*************************************************** 69.4



Figure 8b - This figure shows the calculated time and cost of transmitting a 1
            megabyte file from New York to San Francisco.  Notice how much
            quicker and cheaper it is to use a 28,800bps modem compared to 
            the 2,400bps modem.

* Note:     This is a generalization because actual throughput depends on
            the compressibility of your file and telephone rates may vary by carrier.
            The data in this graph originally appeared on the back of a TWINCOM
            14.4DFi fax/modem box.


























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