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From: ho@hoss.unl.edu (Tiny Bubbles...)
Newsgroups: comp.dcom.modems
Subject: Re: Why does disconnect cause garbage before NO CARRIER?
Message-ID: <1991Feb12.003647.25398@hoss.unl.edu>
Date: 12 Feb 91 00:36:47 GMT
References: <653@twg.bc.ca>
Sender: news@hoss.unl.edu (Network News Administer)
Organization: University of Nebraska - Lincoln
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In <653@twg.bc.ca> bill@twg.bc.ca (Bill Irwin) writes:

>I have had an annoying problem that I would like to eliminate.
>Frequently, although not always, when disconnecting from a
>Unix/Xenix system by entering ^D to log out, a mess of control
>charters is spewed to the screen before the carrier is dropped.

This is caused by the loss of carrier itself.  During that time,
the modem is missing the underlying carrier and spews random
garbage.  It's not the fault of the host system, but rather of the
modem and protocol used.  (For example, local BBS'es would cause
this effect also.)

>I have some systems that I connect to which, upon log out,
>produce no garbage whatsoever - then a NO CARRIER;  and others
>that produce no garbage, but give a new login prompt so that I
>must manually tell the modem to hang up.

1.  No garbage:  Probably your 9600-baud lines, and 2400-baud hookups
which are using an error-correcting protocol such as MNP.  These will
"eat" the trash so that you won't see it on the screen.  In reality,
the modem is waiting for the corrected data to come.  It never does.  
It's told to drop carrier first.

2.  Manually:  The host modem never drops carrier, and you have to hang
up on it.  By definition, if you hang up on someone, the modem "knows"
that you did it.  On the other hand, if the other end hangs up on you,
it takes a while (see below) to figure out that it happened.

3.  #&$*(%(!!^%*(#@ NO CARRIER:  Non-error-corrected lines will exhibit
this behavior.  The garbage comes from the lack of carrier and will last
for a length of time determined by a modem setting.  Try using "ATS10=2"
and see if that reduces the length of the garbage.  If so, that's the
culprit.  (You will never be able to completely eliminate the garbage...
at least, I don't think so.  I'm not a modem engineer.  Toby?)
--
        ... Michael Ho, University of Nebraska
Internet: ho@hoss.unl.edu | "Mine... is the last voice that you will ever hear."
Disclaimer:  Views expressed within are purely personal and should not be
	     applied to the Daily Nebraskan or any university department.