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From: sl@van-bc.UUCP
Newsgroups: comp.dcom.modems
Subject: Re: Answering modems should need no commands! // 2400 answer is fragile
Message-ID: <762@van-bc.UUCP>
Date: Wed, 27-May-87 03:00:33 EDT
Article-I.D.: van-bc.762
Posted: Wed May 27 03:00:33 1987
Date-Received: Thu, 28-May-87 06:20:00 EDT
References: <2130@hoptoad.uucp> <913@runx.ips.oz> <2726@phri.UUCP>
Reply-To: sl@van-bc.UUCP (Stuart Lynne)
Organization: Public Access Network, Vancouver, BC.
Lines: 35

In article <2726@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>In article <913@runx.ips.oz> dave@runx.ips.oz (Dave Horsfall) writes:
>> I get annoyed when making several expensive phone calls to remote
>> machines, hearing the answer tone, then zilch.  If the machine has
>> crashed or is turned off, the modem doesn't know this, and quite happily
>> answers the phone for you.
>
>	I think we're talking about two different things.  On the one hand,
>we have commands -- characters sent over the RS-232 data lines which a
>micro in the modem interprets.  This includes the "ATDT" kind of stuff
>familiar to anybody who's used a Hayes-style modem.
>
>	On the other hand, we have modem control signals, such as DTR (Data
>Terminal Ready) and DSR (Data Set Ready).  A (properly designed) data set
>won't answer an incoming call unless DTR was asserted; this is as true
>today as it was 20 years ago.  The modem control signals are wired such


The simplest way to handle this for a Hayes type modem is to make sure it
does not have auto answer on (ATS0=0). A simple modem watching program can
monitor for RING, send ATA, then wait for CONNECT, and get the SPEED. It
then execs to getty with the proper speed. It also watches for uucp/cu LCK
files so uucp/cu can use the line as long as no one is actually logged in.

The reason for explicitly answering the phone (so to speak) is for
additional security. Your modem will not answer the call UNLESS the mgetty
(my modem program) tells it to. Hanging logins are secure against people
phoning in. The mgetty program can also log out people who have not typed
anything for N minutes.

Another plus of this system is not having to worry about people using break
to get the proper speed with 2400 bps modems.

-- 
Stuart Lynne	ihnp4!alberta!ubc-vision!van-bc!sl     Vancouver,BC,604-937-7532