Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!mailrus!ames!elroy!cit-vax!ucla-cs!casey
From: casey@CS.UCLA.EDU
Newsgroups: comp.dcom.modems
Subject: BYTE high speed modem article and the Telcor Accelerator 2496MA
Keywords: BYTE magazine article, high speed modems, wild compression results
Message-ID: <12997@shemp.CS.UCLA.EDU>
Date: 2 Jun 88 04:08:29 GMT
Sender: news@CS.UCLA.EDU
Reply-To: casey@COGNET.UCLA.EDU (Casey Leedom)
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Lines: 107


  For those who haven't seen it yet, the June 1988 issue of BYTE magazine
has an absolutely incredible article on modems (volume 13, number 6, pages
102-113).  The article is clear, comprehensive, and interesting.  It
covers the current state of modem protocol standards and describes how
some of the most popular high speed modems achieve their performance.

SUMMARY:

  V.32 is a CCITT full duplex 9600 protocol for two wire telephone
lines.  It was adopted in 1984.  It uses echo cancellation to sort out the
interference caused by two senders operating at the same time.
Unfortunately V.32 was ahead of its time and difficult to implement
because it required such sophisticated techniques (high speed signal
processors).

  Many companies responded to consumer demand for an immediately
available high speed modem by modifying another, older CCITT standard,
V.29 (V.29 protocol engines were/are readily available).  V.29 is a full
duplex protocol for four wire lines.  It was adopted in 1976.

  The high speed modems designed around the V.29 engines of course have
to play games in order to operate over two wire lines.  I won't go into
the details here - read the article.  Many of these modems also
incorporate various data compression techniques and almost all of them
have error correction of one form or another.  Again, read the article
for the details - your time will be well spent.

  The article goes on to describe 13 currently available high speed
modems, describing their communication protocols, and compression and
error correction schemes.  It then goes on to reporting the results of a
fairly extensive series of tests which measured the modems' performance
over clean and noisy lines.  At the risk of getting sued for copyright
infringement, I'll include one of the summary tables here:

Manufacturer/			Typical line	Noisy line
Modem				MAX	AVE	MAX	AVE	Protocol
------------------------------------------------------------------------
Case 4696/VS			8429	6422	4925	3274	V.29/V.27
Concord 296 Trellis		8842	8448	8861	8237	V.32 *
Data Race BMX-VM		4963	4704	4829	4339	V.29
Data Race VM I			5520	5136	   0	   0	V.27
Fastcomm Turbo 2496		3475	2486	3341	2102	V.29
Hayes V-Series Smart Modem 9600	5002	4742	4973	4435	V.32 HDX
Microcom AX/9624c		8304	6115	3926	2592	V.29
Racal-Vadic 9600VP		6442	5798	6461	5002	V.29
Telcor Accelerator 2496MA	9091	8256	9082	8362	V.22bis *
Telebit TrailBlazer Plus	7152	5568	7229	5078	PEP
Telenetics 9600E/V.32		9283	8995	   0	   0	V.32 *
USRobotics Courier HST		8678	8083	   0	   0	Asym. TCM QAM
Ven-Tel EC18K-34		7066	5414	7190	4704	PEP

  All MIN/AVE figures are bits per second (bps).  Test is transmission of
81920 bytes of pseudo random data.  Modem/computer connections were fixed
at 9600 baud (the lowest common denominator).  Full duplex modems (those
marked with `*') were tested with full duplex data streams, all others
with data flowing in only one direction (the half duplex modems exhibited
very poor performance when full data streams were running in both
directions).  (The Cermetek, NEC, and Universal Data Systems high speed
speed modems were not available at the time of publishing for the BYTE
article and will be reviewed in a later article.)

COMMENTS:

  As I said above, this is an excellent article and well worth the time
to read it.  The testing results are valuable to anyone considering buying
a high speed modem (though it must be remembered that since almost none of
these modems will talk with each other - availability of other modems of
the same brand to talk to should also be considered for general use
purposes, eg. the Trailblazer for USENET sites).

  One of the most startling results of the review is the performance of
the Telcor Accelerator 2496MA.  Using only 2400 baud protocol technology,
it was second only to the two true V.32 modems tested for average
transfer rates on typical lines, and topped the entire field hands down
on noisy lines.  This to me is nothing short of astonishing.  The Telcor
also appears to be practically immune to noise.  Finally, it had the
cheapest list price ($895) of any of the tested modems.

  The authors of the BYTE article were also impressed with the Telcor's
performance and used it to justify prophecies of 38Kbps modems in the
near future.

  One disturbing aspect of the Telcor is the fact that it accomplishes its
miracles of throughput via a proprietary data compression and error
correction technique.  This bodes ill for the survival of the company
unless they want to drop the price of their modems down to $300.  At the
current price, one's thought is: ``I'll only *ever* be able to talk to
other Telcors.  I wonder how many other people are going to buy one?''

  My advise to Telcor would be to copyright or patent their technique
(whichever legalism is appropriate) and license it out to other modem
manufacturers at the very least.  And if Telcor is truly far sighted, to
simply publish their technique and propose it as a standard.  They'll win
either way in the long run because the consumer will perceive that they
won't be stuck with an expensive 2400 baud modem.  Publishing their
technique would obviously go a lot further along those lines.

FINALLY, QUESTIONS:

  Has anyone gathered any data to support the figures given above,
especially for the Telcor 2496MA?  Has anyone had any experience with the
Telcor?  Would anyone at Telcor be willing to debate the benefits vs.
liabilities of the proprietary nature of Telcor's data compression, error
correction scheme?

Casey