From: geoff@zswamp.UUCP (Geoffrey Welsh)
Newsgroups: comp.dcom.modems
Subject: Re: Question on Hayes ad in Network World magazine
Date: Wed, 09 Sep 92 22:07:25 EDT
Organization: Izot's Swamp

SHUTTERS_WC@TOTO.LAAFB.AF.MIL writes:

> <FLAME ON>

   I'm kinda amused that the flame precedes the questions.  Some readers may 
disagree with Hayes on their statements and some (like myself) think that 
Hayes is being a poor sport for enforcing their rights, but you should know 
the facts first:

> 1.  What is the "time bomb" that the ad talks about?

   A Hayes employee (I believe he was Dennis Hayes' partner, and still might 
be) thought, quite some time ago, that modems used to transfer binary data 
should be very careful about interpreting any code at all as an escape 
code... and yet an escape code was critical to commanding the attention of a 
serial device if you've only got ground, transit, and receive lines connected 
(which is all you *really* need for a modem); he therefore filed a patent 
application for the technique of requiring not only a predetermined escape 
code but also a pause (i.e. no characters transmitted) both before and after 
the data.  This 'guard time' would allow the modem to send the characters in 
the escape sequence as part of, say, a binary download without interfering 
with the modem's operation.  This is not to say that the guard tone guarantees 
that the modem won't fall into command mode when that's not wanted, but it 
reduces the possibility by a large margin. 

   Recently, Hayes has experienced success from lawsuits filed against 
manufacturers who use this technique without paying Hayes a license fee... so 
manufacturers who don't want to pay the fee have simply removed the 
requirement of the silence before and after the escape sequence.  Although 
this sounds like a trivial change, it means that any modem asked to transmit 
three plus signs in a row as part of a message will exit data transmission 
mode and enter command mode, so all characters which follow will be 
interpreted as potential "AT" commands rather than being sent as raw data. 
(Heck, I'll type them here; if you're reading this message on a host that uses 
this patent evasion technique, it'll 'hang' on you unless the escape code is 
disabled: +++) 

> 2.  Is it a "fatally flawed" chip that will actually fail, or is it just a ch
> that isn't licensed by Hayes?

   Neither.  The use of the escape code (vital to compatibility with many 
software packages) without the guard time introduces a serious anomaly in the 
modem's operation.

   This is not to say that these modems can't be put to good use; for 
instance, all of my software uses DTR to put my Hayes Smartmodem 2400 (or 
Telebit 1000) back on-hook, so I disable escape codes entirely.

> 3.  What does the Hayes Patent 4,549,302 cover?

   The use of guard times around an escape sequence to permit a device to 
recognize the difference between the user trying to signal the modem and a 
data transmission which simply looks like the escape sequence.  This guard 
time is critical to making a modem 'invisible' to the data stream though, as 
I said, it isn't a 100% guarantee.

> 4.  Is this ad actually an intimation that Hayes intends to initiate legal
> action against other modem manufacturers who don't or haven't licensed Hayes
> technology?

   The legal action which you apparently fear is yesterday's news.  Most 
manufacturers within reach of the American legal system have either settled 
such a lawsuit with Hayes or lost to them outright in court.  I believe that 
the ad is aimed at those who might consider buying a modem from an obscure 
foreign manufacturer against whom it would be very difficult for Hayes to file 
suit. 

   It is important to note that Hayes is not saying that they are the *only* 
acceptable modem (though the ad suggests that until you read it closely); I'm 
told that U.S. Robotics, for instance, was an early licensee of the 
Hetherington '302 patent and their modems will pass the Hayes escape code 
timing test... as will many others.

Geoffrey Welsh, 7 Strath Humber Court, Islington, Ontario, M9A 4C8 Canada
geoff@zswamp.uucp, [xenitec.on.ca|m2xenix.psg.com]!zswamp!geoff (416)258-8467
         Coincidentally, most people who fight for "fairness" would be
         significantly better off under the system they call "fair"...
Newsgroups: comp.dcom.modems,comp.dcom.fax