Current Shareware 1994 January/SHAR194.ISO/articles/io0893.zip/TECH04.TXT

Text File | 1993-07-30 | 10KB | 217 lines

     Connecting 9600 and Beyond
     Free advice, and "For what it's worth" department:

     By Chip Morrow


     I have been asked about 9600 BPS and beyond more
     times than I care to think about, so the time has come
     to sit down and write a bit on this subject. If you are
     the least bit interested in upgrading to 9600 or
     14400+ BPS, you might find this interesting.

     The only way to talk about this is via a history lesson
     of 9600 BPS as I see it.  Just some observations:

     Many moons ago, the CCITT v.32 standard was not in
     use by anybody, as it was deemed to be too expensive
     to realistically build hardware to support the
     as-yet-unused international standard.

     Modem manufacturers retaliated by building their
     own proprietery 9600 connection schemes, and the
     next thing you knew there were modems all over the
     place that wouldn't talk to any other brand at 9600
     and beyond.

     (If you bought a CompuCom 9600, you had to find
     another CompuCom 9600 to connect to if you wanted
     9600 BPS operation.  Etc. etc...)

     As connect speeds increased, so did errors in data
     transmission.  Anyone who has ever used a
     "standard" modem of the 1200 or 2400 BPS variety
     can verify that you do occasionally experience line
     noise, which shows up as a burst of incomprehensible
     characters on your terminal.  A 2400 BPS modem
     does not use NEARLY the bandwidth that high-speed
     modems do, so you can imagine what happens with
     one of these when you experience line errors.

     That's why "error correction" and "data compression"
     are built into the hardware on most of these things.
     We'll talk about THOSE in a bit here.

     Before all settled down, the one that rose to the top of
     the heap in the BBS world was USRobotics, with
     their proprietery HST modulation scheme, which is
     still in use on MANY bulletin boards today, including
     1 node here.  USR is still widely accepted in the BBS
     community as the leading manufacturer for
     BBS-compatible modems, but there is a price to pay
     (more on this in a minute). USR has since upped their
     proprietery HST protocol to 14,400 bps, and most
     recently 16,800.  Problem is, you NEED a USRobotics
     modem to talk to them at that speed.

     USR does manufacture the "ultimate BBS modem"
     from my viewpoint, and that is the USRobotics
     Courier HST Dual Standard, supporting both their
     HST line, as well as the CCITT v.32 and v.32bis
     standards.  With one of these modems, you can
     connect to virtually any bulletin board in the country
     at 9600 and beyond.

     Perfection has a price, however.  The new Dual
     Standards are retailing for over $1,000 apiece
     (although they can be had for $700 or so thru direct
     channels).  A little pricey from my standpoint.

     Which brings us back to v.32 and v.32bis.  These are
     the accepted international standards for high-speed
     modems, and they are only just recently becoming
     widespread, and supported by MANY modem
     manufacturers. Virtually every modem manufacturer
     EXCEPT USRobotics has devoted their high-speed
     lines to the CCITT v.32 and v.32bis modulation
     schemes.

     Now, back to error correction and data compression.
     You're likely to have heard terms like MNP levels
     1-5, v.42, and v.42bis.  Strangely enough, NOT ALL
     HIGH-SPEED MODEMS SUPPORT THESE.  I have
     seen some low-end v.32 modems that will connect at
     9600 BPS, but with no error correction, meaning that
     your high-speed connections will be unreliable at best.
     Let's talk about these terms for a bit:

     MNP = Microcom Networking Protocol.  There
     didn't used to be any standard for error
     correction/compression, and Microcom's  imple-
     mentation gained wide acceptance pretty quickly.
     Most modems that support error correction support
     MNP.  There are several "levels" of MNP built into
     many modems, even more than I'm going to bring up
     here, but here's what a few of the more common
     methods mean (briefly):

     Levels 1 through 4 = Error correction.  The modems
     negotiate to the highest-supported level on both ends,
     and errors in transmission are "filtered" before they
     get to the remote terminal.

     Level 5 = Data compression.  If "compression" is
     turned on on BOTH ENDS of the connection, and
     both modems support MNP-5, the modems will
     negotiate to this type of connection.  Theoretically,
     this can increase throughput on file transfers.  But, in
     reality, 90% of the files you transfer are already
     compressed (ZIP, ARJ, LZH, etc.), so the overhead of
     this protocol will actually slow you down.

     V.42 = Here comes the accepted international
     standard for error correction.  It is generally felt that
     v42 hookups connect quicker and more efficiently
     than their MNP-4 equivalents. Most modems
     supporting V42 will "fall back" to MNP-4 if a v42
     connection couldn't be made, and to no error
     correction if both fail.

     V.42bis = ...and here's the international standard for
     data compression.  It is generally felt that v.42bis
     performs better than MNP-5, especially on noisy lines.
     Most modems supporting v.42bis will "fall back" to
     MNP-5 if a v42.bis connection couldn't be made.
     v.42bis is more efficient than MNP-5, and you will
     usually see higher throughput than with MNP-5.
     However, this method can STILL actually slow you
     down when transferring compressed files.

     Things to remember:

      You're always limited by the phone lines in your
       area.  If you get static on the line when you make a
       voice call, you can amplify that several times over
       when you make a high-speed connection.  9600+ uses
       just about all of the available bandwidth.

      ERROR CORRECTION is a must.  DATA
       COMPRESSION really isn't, although one tends to
       come with the other on most modems these days, and
       there are quite a few people who will tell you that
       you NEED v.42bis.  I have always seen the best
       transfer speeds with error correction on, and data
       compression off.  The one exception is if you transfer
       a lot of text and/or data files that are NOT already
       compressed.  In that case, data compression really can
       speed up your transfers considerably.

      Most any 9600 BPS modem (including the HST)
       will connect with any other high-speed modem at
       2400 and below.

      USRobotics' HST, like any other modem using a
       proprietery scheme, will connect 9600 and beyond
       only to another USRobotics HST modem.

      USRobotics' HST Dual Standard (the pricey one)
       will connect 9600 and beyond with both their own
       HST's, as well as v.32 and v.32bis modems (which is
       just about the whole high-speed market).  This works
       the other way, too, of course.

      Any modem supporting v.32 should connect 9600 to
       any other modem supporting v.32 (from various
       manufacturers).

      Any modem supporting v.32bis should connect
       14400 with any other modem supporting v.32bis, as
       well as 9600 with v.32 modems.

     My advice:  Stay away from oddball 9600 modems
     that won't talk to anything but other modems from
     the same manufacturer.  USR's HST has a strong
     foothold in the BBS market, but that foothold is
     dwindling.  v.32 and v.32bis are increasingly
     becoming the way of high-speed for the  future.

     Go 14,400 BPS v.32bis, but be careful.  Real-world
     pricing for low-end v.32bis has dipped under $300
     apiece (closer to $200 on some internal models) from
     several different manufacturers (Zoom and Boca, to
     name but a couple).

     If you have a large wallet, get a USRobotics HST
     Dual Standard (*NOT* the cheaper HST model).
     They are very good, reliable modems, and most
     communications & BBS software have setup info for
     them.  They were simply too expensive to be a
     practical option on this end.

     Make sure your system can handle the speed before
     you buy.  You should have at LEAST a 10mhz
     machine (preferably a 286 or better), and at least a
     16450 UART on your serial port, or you're likley to
     start dropping characters.  If you're in a multi-tasking
     environment, or you find yourself dropping
     characters, you'll need a 16550 UART (which has a
     small built-in buffer to help out with this problem).
     Insist on error correction of some type, either MNP-4
     or v.42.  Otherwise, the line noise is likely to make
     life miserable for you.  You'll likely also receive data
     compression with your modem, since one tends to
     come with the other.

     If you aren't transferring text files, turn off data
     throughput on compressed files like .ZIP, .ARJ, etc.
     There are people who will tell you that you'll do
     BETTER with v.42bis enabled, but that hasn't been
     the case in my experience thus far.

     BE WARY OF USED v.32bis MODEMS FOR A
     WHILE.  Rockwell put out a bad set of the v.32bis
     chipsets a while back, and modem manufacturers are
     putting out updated ROMs for these modems at a
     bizare rate.  You want to be able to return the
     modem if it's broken.