Subject: Re: pppd loopback/modem hangup problems
To: None <>
From: Mike Long <>
List: netbsd-users
Date: 01/09/1997 12:06:39
>Date: Wed, 08 Jan 1997 21:37:04 -0600
>From: VaX#n8 <>
>A while back I complained about pppd saying "serial line is looped back".
>Ahem.  Like that ever happens.  Anyway, this happens, usually many times
>in a row, and the only solution is to kill pppd (I was using the demand-dial
>feature) and restart it.  Presto, works fine.  This is talking from
>a NetBSD/x86 to a Linux/x86 box.  If I disable magic number negotiation,
>it connects and then says "Modem Hangup".  This repeats several times,
>as before.  Sometimes I'd get the "looped back" error 10 or 20 times in
>a row (I can grep my messages to generate some statistics if you like...
>seems like it occurs 5-10% of the time or so).

Do you see any lossage if you dialup the linux box directly, i.e. with
tip or kermit?

Have you set the 'modem' option in /etc/ppp/options?

Run pppd with the -d (debug) flag, and post what you get when the
problem occurs. You may need to twiddle syslog.conf first, to send
daemon.debug somewhere useful.

>I have one of the USR 33.6 Sportster modems that has been known to exhibit
>strange "pause" behavior, typically when doing interactive stuff --
>that is, these modems have been known to delay received data for up to a
>minute or two when exposed to typical "bbsing" loads -- user sends a few
>bytes, receives many, etc.

Try disabling V.42 and/or V.42bis, and see if that makes it better.

I use AT&FS2=128 as the init string for my Sportster.  The S2=128 part
of it prevents three '+' chars from putting the modem into AT-command
Mike Long <>     <URL:>
VLSI Design Engineer         finger for PGP public key
Analog Devices, CPD Division          CCBF225E7D3F7ECB2C8F7ABB15D9BE7B
Norwood, MA 02062 USA       (eq (opinion 'ADI) (opinion 'mike)) -> nil