
Using modems without phone lines - mmastrac
http://www.insentricity.com/a.cl/230/using-modems-without-phone-lines
======
rachelbythebay
Modems work with T1 lines? Indirectly, sure, but if you can say that, you can
say that about almost anything. Modems also work with long-haul microwaves and
undersea fiber optics and satellite TWTAs too by that logic.

Try this instead: two modems with a length of flat satin cable plugged between
them. ATA on one, ATX1D on the other (X1 to hopefully defeat dialtone
detection). It worked with a generic 2400 bps modem and a Commodore 1670
perhaps 25 years ago. It should still work now.

------
danelectro
Old pre-PC data systems which had COM (RS-232) ports could be directly
connected to (dumb or smart) terminals by a simple RS-232 cable.

To remotely communicate, each device would need to add a modem to interface
across regular ordinary phone lines. One modem would dial, the other would
answer.

To use a "leased line" having no dial tone, then the dial and answer were
replaced by other modem AT commands, or DIP switch settings to change default
modem behavior.

Using a PC in place of a terminal was a drop-in replacement with a terminal
emulator program like Hyperterminal. By the late '90's most PC's had an
internal modem occupying a COM port# in addition to a regular serial connector
identified by a different COM port# than the internal modem.

From Hyperterminal you could choose which COM port to communicate with, your
serial port could be a local device, and modem was expected to be remote.

When the lesser laptops arrived having built-in modems but lacking serial
ports any more, then you could no longer directly connect to a local RS-232
device. Serial to USB adapters, like USB itself, was not well developed, and
drivers were not available for all operating systems.

A good solution for me was to use an early '90's external fax modem attached
to the local serial device, even though it was going to be a local connection.

Then connect the phone connector on this modem to the laptop's phone connector
locally using a simulated leased line.

IIRC the best simulated leased line I came up with had a couple 9V batteries
in series to provide activity voltage, and the DC was blocked from the other
end by a small capacitor which still allowed the signal frequencies to pass in
both directions.

Analog lines will still support 56Kbaud, but many phone company lines are not
high enough quality, so modern modems down-negotiate automatically.

------
Nexxxeh
For SIP, I wonder if he tried T.38?

