Invisible modems ?

[Rajesh Kirpalani]

I am working with a Sun 386i running SUNOS 4.0.1 with an Amstrad SM2400
modem.  Conventialy an RS232 cable can be used to connect a computer and a
device. A suitable application could send/receive data from the device.

            | SUN | ==== RS232 ===== | Device |

Suppose if we wanted to connect a device to a computer over longer
distances a solution might be to use modems.

 Calling DTE                                               Answering DTE

 | SUN | === RS232 ===| Modem | _ _ _ Tel _ _ | Modem | ==== | Device |

The Sun will always call the device. The modem at the device end is given
the command : ATS0=1 (Answer the phone in one RING).  (I configured the
modem by connecting a dumb terminal and then connecting it to the 'device'
once all the option were set.)

      On the Sun I am using the command :-

           ( stty 2400 ; echo ATD Tel_Number ) > /dev/ttya

The above does not work. The modem does not execute the Hayes command.  I
have successfully used the UNIX program tip and entered Hayes commands.
The reason I cannot  use tip is that it interfers  with the application
that is going to be using this 'device'.  (Application reports problems
about two processes cannot share one port (?))

So  the  solution must dial the 'device'  and remain invisible  to the
application. Can anyone  tell me  why the  modem is not responding  even
though a when a dumb terminal installed instead of the modem  at the SUN;
the command was successfully echoed on the terminal screen.

Does any one know what the problem is ? Any solutions/ideas/pointers would
be most welcome.

Rajesh Kirpalani                                   rajesh at jura.tcom.stc.co.uk
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