WG: serial oob (modem management)

Paul Schenkeveld paul at psconsult.nl
Mon Apr 14 12:15:20 PDT 2003

Hi Arie,

On Sun, Apr 13, 2003 at 09:32:55PM +0100, Arie J. Gerszt wrote:
> Hi Paul
> I managed with mgetty to get a login prompt, with 9600. But after typing
> several commands
> it seems to hang, the connection is still established but the terminal
> doesn't show any
> typed characters.
> What would you think?

If it works for a few commands and then stops, it usually has to do
something with flow control if it's a normal serial line.  I don't
know the gnokii port (and have no hardware to test it) so I don't
know if gnokii supports any kind of flow control and how.  So the
only suggestion I have here is to start with flow control completely
switched off in mgetty.  It's been several years ago that I configured
mgetty for the last time but basically you are looking for something
like -crtscrt to switch off hardware flow control and -ixon to disable
software flow control.

After switching flow control off see how far you get.  Does the
connection persist?  You might loose characters now if one side is
too fast for the other, don't worry (yet) first make sure the connection
doesn't hang any more.  BTW, also pay attention to flow control at the
other end of the connection and make sure it's either correct (ie. the
terminal or terminal emulation must exactly match the modem it's connected
to or switched off).

If you get a connection that doesn't hang anymore, you have to start
configuring flow control.  Always make sure that every two layers
talking to each other have exactly the same idea about it.  Hardware
flow control uses an extra pair of wired in the serial cable and only
spans a connection between two pieces of hardware directly connected
together using a cable (ie. the computer and modem on one side of the

Software flow control (XON/XOFF) works by sending in-band data between
two sides and can either communicate between the computer and the modem
it is directly connected to (if the modem and computer are both set up
to use flow control) or between the two computers at the far end (if both
modems are set up to transparently pass XON and XOFF characters without

One more thing, always make sure that on every single connection (ie.
terminal to modem1, modem1 to modem2 and modem2 to computer) the number
of bits per character, the stop bits and parity bits match exactly.
A mismatch in parity setting for instance could lead to the XOFF being
delivered correctly halting the data but the XON being ignored because
of the wrong parity bit and thus effectively freezing the connection

> Regards,
> Arie

Good luck!

Paul Schenkeveld, Consultant
PSconsult ICT Services BV

> -----Ursprungliche Nachricht-----
> Von: owner-freebsd-isp at freebsd.org
> [mailto:owner-freebsd-isp at freebsd.org]Im Auftrag von Paul Schenkeveld
> Gesendet: Samstag, 12. April 2003 08:36
> An: Kurt Jaeger
> Cc: freebsd-isp at freebsd.org
> Betreff: Re: serial oob (modem management)
> Hi All,
> On Fri, Apr 11, 2003 at 12:07:23PM +0200, Kurt Jaeger wrote:
> > Hi!
> >
> > > > i want to add a serial console with a cellular mobile phone to my
> freebsd
> > > > boxes.
> >
> > [...]
> > > Not so sure about what you are after, but I *THINK* you will need to
> build
> > > ports/comms/gnokii
> > > and then run gnokiid. That should give you a "normal" serial /modem
> interface
> > > to the phone.
> >
> > The problem is probably the other way round ?
> >
> > How does one call the mobile phone in such a way that it accepts the
> > call and acts like a serial modem to the computer ?
> >
> > A normal serial line on a nokia can be used as an outdial modem.
> > The problem is: How to use it for a dial*in* ?
> First see if the Nokia allows setting up the modem to auto answer
> the call.  In Hayes lingo one would send
>     ATs0=2
> where 2 is the number of rings after which the modem auto answers,
> 0 meaning don't answer automatically.
> If this doesn't work, see if the modem tells you when a call comes
> in, usually with the message RING (you can tell this by using tip
> or cu to get an interactive session to the modem and then dial the
> number of the Nokia from another line).
> If the Nokia shows the RING message you can still have your
> auto-answer by using the mgetty+sendfax port.
> > --
> > MfG/Best regards, Kurt Jaeger                                  17 years to
> go !
> > LF.net GmbH        fon +49 711 90074-23  pi at LF.net
> > Ruppmannstr. 27    fax +49 711 90074-33
> > D-70565 Stuttgart  mob +49 171 3101372
> Good luck!
> Paul Schenkeveld, Consultant
> PSconsult ICT Services BV

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