Possibilities - V.FC 28.8k Modems, Notes from the eSoft Lab... 12/93

Contact:   eSoft, Inc. (Makers of TBBS)
           15200 E. Girard Ave., Suite 3000
           Aurora, CO  80014
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V.FC 28.8K MODEMS, NOTES FROM THE ESOFT LAB... 12/93
----------------------------------------------------

*** From December 1993 Possibilities Newsletter ***
*** Copyright 1993 by eSoft, Inc.  All Rights Reserved ***

There is a lot of hysteria going around about the new high speed V.FC 
modems.  Claims of transfer rates faster than slow LANs over phone lines are 
showing up in marketing literature, and most non-technical people (and more 
than a few technical types) are confused about what these new modems are 
really offering.  So before discussing how TBBS handles these modems, let's 
first take a hard look at the truth of V.FC modems

The V.FC modem is an emerging industry standard for modems which go faster
than the V.32bis speeds of 14.4kbps.  In fact, their base carrier rate is 
exactly twice as fast -- the top speed of V.FC on a dial-up line is 
28.8kbps, and there are "fall-back" speeds of 16.8k, 19.2k, 21.6k, 24k, and 
26.4kbps.  In addition, the Rockwell chip set which supports this modulation 
scheme is available in some lower priced versions which only have a top 
speed of one of the lower fall-back speeds (typically 19.2k and 24k bps) 
which are used in some brands of V.FC modems.  The first item of interest is 
that regardless of the top speed a specific V.FC modem provides, all brands 
of V.FC modems will communicate with each other at the new, faster speeds.

What speed does data really go?
-------------------------------

The main source of confusion (and the widely varying speed claims) stems 
from the fact that data compression is used where possible to speed up data 
flow through these modems.  If the compression manages to compress the data 
fed to the modem by a 2:1 ratio (much like when you ZIP a file and it gets 
smaller on disk) the compressed data is sent at the modem's carrier rate, 
but the effective speed at which the uncompressed data appears to flow 
through the modem will be doubled.  However, not all data will compress the 
same as other data -- and data which is already compressed (such as ZIP 
files) will not compress any more at all.  So when you gauge the speed a 
modem will transfer data, you have to know what type of data you are talking 
about.

This has been true for all V.42bis and MNP 5 modems for some time, but Hayes 
has added an improved compression algorithm to their Optima 288 that can 
compress text data nearly twice as well as V.42bis alone, prompting huge 
speed claims in their advertising.  While V.42 compresses text files a 
maximum of 4:1, the Hayes extended data compression can achieve a nearly 8:1 
compression on the same text.  So with text only, two Hayes Optima 288 
modems will send the data four times as fast as a V.32bis/V.42bis modem 
(double the carrier speed and double the compression ratio).  Note, however, 
that with a V.FC modem that only has V.42bis compression, this extra 
compression disappears.  In any case data compression is not very important 
in most BBS settings since the bulk of the data transferred is already 
compressed in an archive file.  Where you will see the compression come into 
play is displaying menus and text files to the screen -- the extra "snap" is 
very noticeable.

To really know what to expect from these modems though, you should first 
compare the non-compressed speeds, as this is the slowest the modems will 
ever transfer data.  For all V.42 based modems, there is a speed increase 
beyond the carrier rate which comes from the V.42 protocol itself (not 
compression).  Thus a file which cannot be compressed at all will transfer 
data at a bit less than 20% faster than the carrier rate (1.185 times the 
carrier speed gives a good estimate of the non-compressing speed of a V.42 
modem).  You see this when a 14.4kbps modem gives you a 1700cps transfer 
rate for a ZIP file (1440cps * 1.185 = 1706cps).

Since V.FC modems have several fall-back rates (which we will discuss below) 
the following chart will let you know the actual non-compressing transfer 
rates you can expect to see with compressed files:

Carrier Speed		Non-compressing Xfer in cps
-------------           ---------------------------
14.4kbps			1706cps
16.8kbps			1990cps
19.2kbps			2275cps
21.6kbps			2559cps
24.0kbps			2844cps
26.4kbps			3128cps
28.8kbps			3412cps

Note that individual files may go a bit faster or slower than this (just as 
you see with 14.4kbps V.32bis modems) but non-compressible files will center 
around these numbers.  You will find that by doing a download and watching 
your cps meter you can see the modem change carrier speeds as line 
conditions vary, and even tell what speed it switched to just by the 
transfer rates.

eSoft Test Results...
---------------------

Enough with the theory, how well do they work?  The first full speed V.FC 
modem to reach the marketplace is the Hayes Optima 288.  Zoom is also 
shipping a V.FC modem using the 24kbps top speed version of the V.FC chip, 
and many other manufacturers will soon be shipping their V.FC modems.  The 
tests that eSoft conducted were all done with beta test versions of the 
Hayes Optima 288 modem.

V.FC modems that run faster than 21.6kbps are really looking to find a 
"better than spec" telephone connection.  So the question arises, "in the 
real world, what kind of speeds do I reliably see?"  Our testing on this 
issue is preliminary, but we've tried to do a lot of it in the time we had 
available.

Local Calls...
--------------
What we see is that on cross-town connections you can really get a 28.8kbps 
connection about 80% of the time.  Some particular central offices will not 
do this as often, and tend to only give you a 24kbps connection. It can 
sometimes take two or three calls to get the maximum connect rates. 16.8kbps 
was the lowest we ever saw with 21.6kbps or better being a near certainty.

Long Distance Calls...
----------------------
Long distance calls seem to fall into categories based on where in the 
country you are, and where you are calling.  But even here, it seems to vary 
day to day.   All circuits we tried were usually capable of 24kbps and this 
was the most frequent connect speed we saw.  We did manage to get some 
28.8kbps connects on every circuit we tried.  Some circuits did this easily, 
with only one fall-back on "bad" calls, while others did this rarely and 
were more likely to give 21.6kbps and 24kbps connections.

Automatic speed adjustment...
-----------------------------
One very nice feature of the V.FC modems is that they "fall forward" without 
a significant delay.  So if the lines "get better" the modem will switch to 
a higher speed automatically.  In our testing we saw this happen frequently 
and there was no evidence of any problems with the modems staying "in sync" 
with each other through this process.   When the modems "fall back" to a 
slower speed they do a full retrain operation the same as a V.32 or V.32bis 
modem so there is about a 30 second stoppage in data flow when the speeds 
are reduced.  Again, the retrains seemed to have no problems losing 
connections and overall this process looks to be as good as or better than 
the V.32bis modems in similar circumstances.

Overall Assessment...
----------------------

These modems are hot!!!  They represent another large leap in transmission 
speed and they make yet another category of applications realistic to do 
online.  The V.42bis text compression makes an average text file transfer at 
7000-8000cps (25% faster than ISDN speeds) so menus and other text displays 
"snap".  In fact, they are usually limited by the terminal software's video 
display speed which is almost always slower than the transfer speeds for 
most terminal programs.  We transferred some large TDBS .DBF files (some of 
the most compressible real world files) and saw transfer speeds as high as 
11,200cps!  But in the real world of BBS use, compressed files are the norm, 
and the 3300cps speed is what really counts.

As expected, these speeds are double a V.32bis modem and the difference is 
enough to emotionally affect you when you see it.  Even with a 57kbps 
interface, these modems will provide a full 3300cps transfer rate for 
compressed files, and a 5600cps or better transfer rate for menus and text.

The TBBS V.FC Speed Kit...
--------------------------

These modems require high speed interfaces to achieve full throughput.  As 
shipped, TBBS 2.2 will only support modem port speeds up to 38.4kbps.

eSoft has released a V.FC high speed enhancement kit that you may download 
at no charge from the support BBS mod section.  This kit is in a file named 
VFCKIT.ZIP.  This kit allows you to add either 57k or 115k interface support 
to TBBS 2.2.  Instructions on how to install the kit are in the VFCKIT.ZIP 
file.The modifications included in this kit provide 100% support for V.FC 
modems. TBBS 2.2M has the performance capacity to handle these new ultra-
high speed V.FC modems extremely well.  With the update kit you can also 
handle other higher speed applications (such as ISDN adapters, etc.) as well 
as  hard wired high speed terminals.  Note:  YOU MUST HAVE 16550 UARTS ON 
YOUR SERIAL PORTS TO HANDLE THESE SPEEDS!

How Well Does TBBS Handle High Speeds?
--------------------------------------

eSoft has been conducting laboratory testing on high speed interfaces to 
TBBS 2.2M to determine the raw data handling capacity of TBBS.  Our results 
show that TBBS can support such interfaces very well indeed.  Here are some 
rough outlines of what we have measured:

1.  With a 33Mhz 80486 computer that has no disk caching, a 20ms or faster 
IDE disk drive, and a 128k CPU cache (a low end 486, and a fairly "average" 
computer in today's market), we find that TBBS 2.2 can support the following 
speeds with no slowdown under full loading:

	o Four 115.2k (hard wired interfaces) or

	o Nine to Ten 57.6k (hard wired interfaces) or

	o Thirty-two V.FC modems transferring compressed
	  files at 3300cps simultaneously.


2. A 50Mhz ISA bus 80486 with a caching SCSI disk controller and a 256k CPU 
cache (the high end of "lower cost systems") can support the following 
connections with no speed loss under full load:

	o Nine to Ten 115.2k (hard wired interfaces) or

	o Twenty-four 57.6k (hard wired interfaces) or

	o All the V.FC modems you can hook up.


3. A 66Mhz Local bus 486 with a caching SCSI local bus disk controller can 
support the following connections with no speed loss under full load:

	o Twenty-eight 115.2k (hard wired interfaces) or

	o Over sixty 57.6k (hard wired interfaces) or

	o All the V.FC modems you can hook up.

Note:  These ratings are the typical conservative "eSoft numbers" for 
performance.  They mean that you can pump data all day on all lines at the 
same time at full speed with less than a 10% speed loss at any moment.  In 
the real world, you can hook much more than this to a TBBS and see 
performance that you will not think of as degraded in any way (i.e. the kind 
of specs everyone else uses!).  So when you compare this to the kind of line 
counts at a given speed that other software claims, you can know that with 
equal performance to those systems TBBS will support nearly double the 
numbers given above on a given hardware configuration.  But if you want to 
win bets in a "metered environment" these are the numbers.

We have never set up to measure TBBS data handling capacity at these high 
speeds before, and even though I know that TBBS is the most efficient 
software on the market I was astonished. This is absolutely the best serial 
data performance of any software that has ever been created for computers of 
any kind (notice I'm a bit stoked at how the lab tests turned out -- you'll 
be happy with the results in the real world too).

I can say with confidence that no other BBS software on the market can feed 
this much data to serial ports at these speeds on a single CPU.  Most cannot 
even come close.  Those who use one-copy-per-node systems (such as WildCat! 
and PCBoard) will be able to drive these modems fully only by adding more 
computers (say goodbye to DesqView).  With TBBS you can just plug in the 
modems, install the upgrade, and watch the data flow!  You have the only BBS 
software available for which that is true.

PS1293-1
Rev. 12/93

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.

