modem mileage

[Jim Gottlieb]

In article <1991Feb17.122852.26711 at world.std.com> dcc at world.std.com (Dave C Curado) writes:
>
>and we must always call
>in to the machine via good ol' 2400 baud modems.  This works fine, until
>you have the occasion to drop the session in an ungraceful sort of way...
>When this happens, it seems as if the modem freeks out and sits there
>trying to communicate with the shell process I've left running.

This can usually be avoided by keeping the modem set to echo off
(ATE0).  This has solved all of our "deadly embrace" problems.  Also
make sure that the modem drops CD and DSR upon loss of carrier.

But on to the broader subject...


>280 miles later, (two round trips to go and fix the problem)
>my tires and I are looking for a 'better way.'
> Some ideas we've had:
>    - try to make a daemon that would watch for this sort of tie up, and would
>       kill the process.

We have voice mail machines sitting in closets all around the country.
There is no one there to help out if anything goes wrong, and I don't
like hopping a train or plane to go reboot a hung machine.  So we have
many failsafes.

We designed and built a board that sits connected to the speaker leads
of the machine.  A daemon process sends a beep to the speaker every
minute.  If the board goes for 10 minutes or so without hearing
the beep, it shorts the reset leads together.  This takes care of a
total machine hang.  Of course we also modified /etc/dumpsave so that
the machine will always reboot.

We are a large consumer of X-10 modules.  These are devices that plug
into the wall and can be controlled by (among other means) a remote
telephone call.  We plug the computer and the modem each into their own
X-10 appliance modules.  This allows us to power down and back up the
modem (first resort) or the computer (last resort).  Our medium resort
is the X-10 module that gives a momentary contact closure.  This is
bridged across the reset leads. 

I would much rather just do a hard reset than a powerdown (basically
pulling the plug), but sometimes the voice boards get into a state
where they need to be powered down.


By using these methods, most field visits can be avoided.

Radio Shack carries X-10 products under the name "Plug'n'Power", but I
don't think they carry the Telephone Responder.  You can contact X-10
directly on 800-526-0027 or +1 201 784 9700, but you'll pay full list.

--
Jim Gottlieb	Info Connections, Tokyo, Japan
E-Mail: <jimmy at denwa.info.com> or <attmail!denwa!jimmy>
Fax: +81 3 3237 5867   Voice Mail: +81 3 3222 8429