Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site fortune.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxn!ihnp4!fortune!mats
From: mats@fortune.UUCP (Mats Wichmann)
Newsgroups: net.bugs.uucp
Subject: Re: Modem doesn't hang up after uucico on some sites
Message-ID: <5821@fortune.UUCP>
Date: Fri, 27-Dec-85 10:35:27 EST
Article-I.D.: fortune.5821
Posted: Fri Dec 27 10:35:27 1985
Date-Received: Sat, 28-Dec-85 01:45:19 EST
References: <115@sat-bc.UUCP> <478@uwvax.UUCP>
Reply-To: mats@fortune.UUCP (PUT YOUR NAME HERE)
Distribution: net
Organization: Fortune Systems, Redwood City, CA.
Lines: 42

Oh, boy, this is fun. Now I get to flame at cheap modems again.

There was a time when a modem was a device that handled your
phone lines, and an autodialer was a separate device which
connected to one of your available modems and made the call for you.
Then there were personal computers, bringing with them personal
modems. What a bunch of neato folks did to their modems was put
the capability to accept commands typed on your terminal
(or for loons like us, sent by the system software) and use them
to try to establish the connection. What is wrong with this?

Well. modems have the characteristic of only supplying a ready
signal to the outside world when a connection is established.
This is good and proper behavior - you don't want to try to
talk through the modem until there is something on the other
end. But the poor terminal/system can't even send the "transparent" 
commands to the modem until it sees this ready signal - like you
can't send out the commands to establish the connection until
the conenction is established (don't they call this Catch-22?). 
So what to you do? Well, the modem makers tie the signal permanently 
high so they can guarantee the terminal can always talk to the modem's
ROM and make it dial.

Of course, once you have done this, you have broken the modem
as far as auto-answer, becuase your carrier line never changes
state (we just finished fixing it to be permanently on, remember).
Most modems built these days are at least social enough to
give you a switch to select the way this works - either force
the line high (for dialout) or leave it indicating the status
of the connection (for dialin). The first modem I ran into
with this clever mod was a Racal/Vadic which didn't bother
to give you a switch - you had to get inside the mother and
cut a trace on the PC board!!!

Moral of story - if using affordable equipment, make sure it is
affordable enough that you can buy two - one dialin and one dialout.
Otherwise empty your bank account buying a modem with an external
dialer. Sorry, not an elegant solution.

    Mats Wichmann
    Fortune Systems
    {ihnp4,hplabs,dual}!fortune!mats