From: lee@dlpco.dlpco.COM (Lee Penn)
Newsgroups: biz.sco.general
Subject: Re: What causes modem to hang system?
Date: 7 Sep 92 14:54:40 GMT
Organization: [resent by] The SCOGEN gateway and Propagation Society
Resent-From: mmdf@xenitec.on.ca
Submit-To: scogen@xenitec.on.ca
Precedence: bulk

>From uunet.uucp!xenitec.on.ca!news Mon Sep  7 06:16:14 1992
>To: distribution@xenitec.on.ca
>Newsgroups: biz.sco.general
>Path: xenitec!news
>From: "xenitec.on.ca News Administrator" <xenitec.on.ca!news@uunet>
>Subject: Re: What causes modem to hang system?
>Submit-To: scogen@xenitec.on.ca
>Organization: [resent by] The SCOGEN gateway and Propagation Society
>Date: Mon, 07 Sep 1992 03:33:47 GMT
>Message-Id: <1992Sep07.033347.5645@xenitec.on.ca>

>Lee Penn writes:
>> If your modem has lights, you will probably see the send and 
>> receive lights blinking like crazy.  The modem is sending 
>> messages to the computer which is being passed to login.  Login 
>> is failing and starting another login and so forth.  The login 
>> process is going crazy.
>> 
>> Solutions:  1) Be sure echo is off so the modem will not echo 
>> "login:" back to the computer which confuses login into thinking 
>> that someone called login is logging in.
>> 
>> 2) Be sure and turn off responses as login can think that RING is 
>> a user also.

>> I run our modems with ATQ1 and ATE0 which turns OFF responses and 
>> echo respectively.
>> 
>> Also make sure your CD and DTR signals are being properly handled 
>> by the modem.

>I don't get that, I don't get it at all, at all, at all...

>With Telebit, Practical Peripherals, or Viva modems:
>  Under Tandy Xenix, SCO Xenix, or SCO Unix:
>    ALL my modems have ALWAYS been set (in NVRAM, yes):  &c1 &d3 q0 e1
>      I have always run my ports DIDO, and no login has ever failed,
>      nor has any outgoing uucio, cu, or xc, ever not worked, with
>      those settings of the modems.

>Why do so many folks advocate make a mute out of the modem???
>I've never done it, and it's never confused any getty.

>-- 
>Jean-Pierre Radley   Unix in NYC   jpr@jpr.com   jpradley!jpr   CIS: 72160,1341


I've seen this problem over and over again.  It may also be the 
improper use of modem control ttys vs non-modem control ttys.  If 
getty thinks there is an active line coming in, then the modem 
responses will appear to getty like a login attempt.  Then, of 
course, getty sends a password request which the modem echoes 
right back to the system which is interpreted as a password entry 
which, of course, fails.  SO... getty sends a login which is 
echoed back by the modem and getty things a person with "login" 
is logging in...  Out goes a password request and so on and so on 
and so forth.  The send and recieve lights are going crazy and 
the system is at a dead stop or close to it.  The easy fix is to 
make the modem mute.

Another source of this problem is that people attach modems with 
CD forced on rather than acting properly.  Then, even if the 
proper modem control port is used, there will still be a problem.

I've also seen where the messages sent by the modem as a 
connection is made, RING, CONNECT, etc will cause a modem to 
simply chop off a user.  The complaint is always that the user 
gets a CONNECT when dialing in followed by an immediate loss of 
Carrier.  This is again caused by a non mute modem.

All modems are different.  Every time we try to use a different 
modem, we have a learning curve to discover the peculiarities of 
that modem.  Rather than fighting thru the modem documentation, 
we make the modem mute with ATE0 and ATQ1 and then change what 
other settings we need to make DTR and CD behave logically.  
"Logically" is totally dependent on the modem by the way.  

Practical Peripheral modems like to turn auto-answer off when 
there is a CD transition.  You have to program the modem to avoid 
this problem.

It would be nice if SCO would have standard documentation on each 
possible modem a user might buy as to the proper setup for 
precision operation.  You know...  given that the Telebit is so 
popular, it is really strange there there are so many different 
ways to set on up.

BTW: We do not make the Telebit's mute as they are mute when in 
ANSWER mode.  Not all modems are mute in ANSWER mode which is why 
we choose to make such modems mute.  You only want chatter from 
the modem when the modem is operating in originate mode.

================================================================================
Lee Penn,  DLP Technologies, Inc.                     Voice: 513 232-7791
SCO Advanced Product Center                           FAX: (513) 232-7801
7444 Jager Ct.
Cincinnati, OH  45230-4344                           email: lee@dlpco.COM