Modem monitor

[Rodrigo Amaral]

Hello ALL!!!

I have 2 computers in modem communication. I need to monitor that
communication using a 3rd computer. May I use a 3rd modem (with a high
impedance interface) to do the job?

If not, which are the suitable methods?

[Bruce (zcat@coders.ml.org)]

: I have 2 computers in modem communication. I need to monitor that

: communication using a 3rd computer. May I use a 3rd modem (with a high
: impedance interface) to do the job?

Only for very slow (2400 bps and less) modems.. at faster speeds both
modems use the same ste of frequencies, and sort out who said what using
'echo cancellation'. It's just about impossible to pick one side from the
other without special equipment.

You can tee off TD or RD from the serial connector at one end, this will
give you half the traffic. To monitor traffic in both directions, connect
the TD and RD lines from the modem at one end of the link to the RD lines of
two different serial ports on your monitoring machine. Or get a proper comms
analyser.

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[David Bowerman]

r...@omega.barralink.com.br wrote in a message to :

ro> I have 2 computers in modem communication. I need to monitor
ro> that communication using a 3rd computer. May I use a 3rd modem
ro> (with a high impedance interface) to do the job?

No. The two modems are using the same bandwidth and echocancelling to sort out
which modem is talking to which.

ro> If not, which are the suitable methods?

I would suggest an RS-232 butt-in box which allows you to monitor the RS-232
send/receive lines on one of the computers. The box I used allows you to
monitor Tx, Rx or both on a third computer. This will work unless you actually
need to look at the raw transmitted packets that get transmitted with an
error-correcting connect.

Regards,
David

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