Re: Re: Script to check whether modem telephone line in use --- how?

[David Wright <d.wright@open.ac.uk>]

Quoting Mark Phillips (mark@ist.flinders.edu.au):
> > On Wed, Mar 31, 1999 at 11:41:47PM -0600, Bud Rogers wrote:
> > > Mark Phillips <mark@ist.flinders.edu.au> writes:
> > > 
> > > > I hope this explains now why I was trying to write a script that would
> > > > actually allow me to hear what was on the phoneline, enabling me to
> > > > determine if my father was actually using it.  (At the moment the only
> > > > way is to physically go upstairs and check his computer/ask him.)
> > > 
> > > Put ABORT "NO DIALTONE" in your ppp chat script.
> > 
> > In my experience, the noise of the line being picked and up dropped
> > by the other modem will interfere with the session -- it will almost
> > certainly cause the modems to retrain, and may cause them to hang up.

That's not my experience with USR 33.6 modems and linux; the retraining,
yes; hanging up, no.

> When the situation is reversed (I am running ppp and my father started
> dialing under windows), if he stops the dialer quickly enough after
> hearing the noise on the line --- if he stops it before it starts
> dialing, he can usually get out without disrupting my ppp link.  I
> can't do this in linux because poff takes a while to stop things
> whereas under windows you can stop immediately.
> 
> The point then is, that in my experience, it might be possible to
> listen to the line without disrupting the other link.  The other
> evidence in favour of this is that I can pick up a normal phone,
> listen to the link, and then put it down again --- without disrupting
> the ppp link.  (Of course you have to keep quiet.)
> 
> Oh, and I tested out my idea for a script by using minicom.  First I
> did
>        atm2
>        OK
> but I couldn't hear anything.  Then I did
>        ato
>        ERROR
> and also tried
>        ato0
>        ERROR
> My guess is because I hadn't actually connected anywhere via the modem,
> I couldn't actually go online.  Anyway, I haven't been able to find a way
> to listen to the line.
> 
> Actually, perhaps I could try
>        atd
> without actually specifying a number.  I wonder if this would work??

Presumably you need ATH1 to go off hook. The modem speaker is not
active otherwise.

> > Some sort of "line in use" indicator would be better.
> 
> I presume you mean a hardware "led indicator" or something like that?
> I could do that, though I'd prefer a software solution if there is
> one.  
> 
> (And I am also curious as to why the  ABORT "NO DIALTONE" doesn't seem
> to work --- I always thought it did abort, but just took its time
> about doing so --- ie only after it had dialed the number and waited
> a while.  But from what Bud Rogers has said, it would seem the abort
> should happen straight away.)

This is a modem issue. When confronted by so much whistling and warbling,
it probably doesn't know what to think. I guess that enough signal
emerging from a particular spectrum filter is enough to convince it of
a dial tone. After all, a (quite common) initial triple ringing tone
before the familiar double one (in the UK) is enough to make mine
think that the other end is busy, and there's nothing the software can
do about it.

Just a thought, but over here, a second line is quite cheap.

Cheers,

-- 
Email:  d.wright@open.ac.uk   Tel: +44 1908 653 739  Fax: +44 1908 655 151
Snail:  David Wright, Earth Science Dept., Milton Keynes, England, MK7 6AA
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