Re: [TECH] Modem-to-Modem wire connection

From: Peter Sin (
Date: Sun Apr 23 2000 - 20:33:38 CEST

      I have tried a few experiments. I noticed that
I have two kinds of "standard" telephome cables
(I am in Florida, US by the way). They have the same
connectors but one kind has four conductors and the
other kind only the two middle ones. The ones with
two conductors came with my modems.

My guess is that the two middle wires are transmit and receive while the
outside ones have to do with handshake
signals. So I tested the connections. With the
two-wire cable, the connection seems to work fine
for all settings of the modems (I did not check for
packet loss etc however, which may happen at higher speeds). For the
Four-wire cable, the connection
works only when hardware handshake is enabled on both
sides. I also tried with a pcmcia card modem
in a laptop (which has a two wire cable) and it also works.

This is probably irrelevant, but
one time the modem complained NO DIATONE
when I entered ATD so istead I enetered ATA on that machine and ATD on the
other, which fixed it. (I think ATX1to ignore dialtone would work too.)

I think that's about all I can sensibly say.
Perhaps there is a telco engineer in the list who can help?
I would be glad to carry out any further experiments which you think might
shed more light on the problem.

Best regards,

> Crossover is normal for digital signal, but I'm not totally sure
> if this apply also for modem cable, because modem is a digital-2-analog
> converted, in crude words and ( we know) analog signals are
> indifferent to crossover problematic. On the other hand, I do not
> know if one specific pin is used fro handshaking and similar.
> I connected the two modem as you explained, but I havn't got a
> connection yet.
> Michele
> --
> I'd like to conclude with a positive statement, but I can't
> remember any. Would two negative ones do? -- Woody Allen
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