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Date: Thu, 4 Mar 2010 15:32:15 -0600 (CST)
From: Robert Bonomi <bonomi@mail.r-bonomi.com>
Message-Id: <201003042132.o24LWFhW018772@mail.r-bonomi.com>
To: freebsd-questions@freebsd.org
Subject: Re: RS232 / TCP converter and BSD.
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> From owner-freebsd-questions@freebsd.org  Thu Mar  4 10:41:36 2010
> To: freebsd-questions@freebsd.org
> Date: Thu, 04 Mar 2010 10:41:00 -0600
> From: Martin McCormick <martin@dc.cis.okstate.edu>
> Subject: Re: RS232 / TCP converter and BSD. 
>
> Chuck Swiger writes:
> > Data centers use that for serial connections to stuff like Cisco routers
> > and other terminal applications all the time. However, if the device is
> > truly RS-232 rather than 422/423, it's nominally out of spec past 50 
> > meters
> > and possibly won't go past 9600 baud.
>
> 	I was wondering about that when I wrote my long-winded
> response. I was confused and thought the maximum length for
> RS-232 was longer than it is. 70 meters is almost 25% out of
> range which is kind of pushing things.

The 'standard' way to get around that distance limitation is to use a
"RS-232 to current-loop" adapter, often referred to as a 'short haul modem'.
see: <http://www.blackbox.com/Store/Detail.aspx/Short-Haul-Modem-Nonpowered-Async-SHM-NPR-DB25-Male/ME721A-M-R3>

for one example from a quality, but fairly pricey, source.

Note: you need one of these on each end of the wire.